Basilica of İznik

The Basilica of İznik consists of submerged remains of an early Christian-era church with a basilical plan, located approximately 50 metres offshore and at a depth of 2–3 metres within the boundaries of Selçuk neighbourhood, İznik district, Bursa Province, beside İznik Lake. The structure lies just outside the lake-facing section of the ancient walls surrounding the city of Nicaea, situated in the transitional zone between the city’s land walls and the lakeshore, aligned parallel to the coastline. This positioning indicates that the building was directly integrated into both the urban layout and the topography of the lakeshore.

The remains were identified in February 2014 during aerial photographic surveys conducted in İznik and its surroundings by Professor Dr. Mustafa Şahin. Distinctive wall traces, aligned parallel to the shore and forming a near-rectangular shape, became visible in the aerial images, prompting on-site verification. Subsequently, under permits issued by the Ministry of Culture and Tourism, underwater research was initiated on behalf of Uludağ University. Following the announcement of the discovery, various reports on the structure were published in national and international media; the existence of a submerged basilica along the shores of İznik Lake has emerged as a new area of research within the contexts of early Christian architecture and underwater archaeology.

The area where the remains are located is traditionally associated with the site where Saint Neophytos, believed to have been martyred in the early Christian period, suffered torture and death near the lakeshore. It is stated that after Christianity was officially permitted, a church dedicated to the saint was constructed in this area. Current archaeological evidence suggests that the submerged basilica may be connected to this tradition and may have functioned as a sacred site dedicated to Saint Neophytos.

In the period following its discovery, surface underwater surveys were first conducted, followed by systematic underwater excavations. Under the leadership of the İznik Museum Directorate and with scientific guidance from Uludağ University, floating platforms were established on the lake. Specialized underwater archaeological equipment—including diving operations, snuba systems, centrifugal pumps, and sieving units—was employed. This enabled the controlled removal of sediment from the lakebed, precise documentation of architectural remains in situ, and detailed recording of small finds.

Research revealed that the basilica’s plan, nave arrangement, apse location, and associated architectural elements are largely discernible. Additionally, coin, ceramic, and other small artifact groups recovered from the site have become primary sources for determining the chronology and phases of use of the structure. The İznik Lake Basilica, through these characteristics, constitutes a critical example both for understanding the Christian-period topography of İznik and for the development of underwater archaeology practices in Türkiye.

Location, Natural Environment, and Geomorphological Context

The Basilica of İznik is situated on the northeast shore of İznik Lake, in the southeastern part of the Marmara Region, approximately 20–30 metres beyond the lakeside section of the modern İznik settlement’s ancient walls. The architectural remains extend parallel to the shoreline, averaging 50 metres from the current coastline. In this section of the lake, depths range between 2 and 3 metres; the calm and relatively shallow water allows the remains to be clearly visible on the lakebed.

İznik Lake formed on a tectonic depression. This depression, aligned parallel to the southern branch of the North Anatolian Fault, has undergone continuous geomorphological changes throughout history due to seismic activity. The ancient settlement of Nicaea on the eastern shore was directly affected by this seismic instability; geological evidence supports that the shoreline shifted inland or outward at different periods during antiquity. Measurements of the lakebed indicate particularly significant sediment accumulation along the northeast shore, suggesting that the historical coastline may have been located farther inland than it is today.

The geomorphology of the area where the basilica is located is closely linked to fluctuations in lake level and earthquake-induced subsidence. Chronologies of settlements around the lake and records in ancient sources indicate that the lake’s water level varied by at least several metres during historical periods.

The submergence of the basilica is likely linked to a major seismic event during the Late Antiquity or Early Medieval period. The earthquake of 740 CE, documented in Byzantine sources as having caused extensive destruction in Nicaea, is considered one of the primary events responsible for the structure’s submersion beneath the lake waters.

The hydrological structure of the lake’s surroundings also directly influences the preservation conditions of the remains. İznik Lake is a closed basin with no significant current systems beyond minor surface runoff from surrounding streams and groundwater inflows. As a result, thick accumulations of mud and fine sediment have formed on the lakebed, largely preserving the wall fragments of the basilica within this soft sediment layer. This sediment cover has surrounded most of the building’s masonry, slowing erosion and contributing significantly to the relatively good state of preservation of the remains for underwater archaeology.

Bathymetric measurements around the remains indicate that the lakebed slopes gently downward toward the northwest. This slope highlights the plateau-like shallow area on which the structure is situated. The irregular distribution of stone blocks farther from the main structure suggests that long-term water movements and microscopic slippages on the lakebed have partially altered the original positioning of the remains.

In terms of natural environment, the coastline where the basilica is located lies near the eastern gate of the ancient city of Nicaea. It is presumed that a small harbor or pier structure existed in the area where the road exiting this gate reached the lakeshore. In this context, it has been suggested that the basilica’s proximity to the shore was not solely of religious significance but also related to the city’s access to the lake. The location of this sacred structure in the northeastern sector of the lake marks a transitional zone between land and water routes within Nicaea’s urban topography.

Discovery, Research, and Excavation History

The remains of the Nicaea Lake Basilica were identified in February 2014 during aerial photographic surveys conducted by Professor Dr. Mustafa Şahin. During this study, aimed at documenting ancient settlement traces in and around Nicaea, a rectangular structure silhouette was detected just beneath the water surface near the lakeshore; parallel wall traces indicated that architectural remains might be preserved on the lakebed. Subsequent on-site inspections revealed the foundation remains of a basilica-style church approximately 50 meters from the lakeshore and at a depth of 2–3 meters. In the same year, the American Institute of Archaeology’s periodic publication Archaeology magazine included these remains in its list of the “Top 10 Discoveries” of 2014, thereby recording the structure in international literature.

In the initial phase following the discovery, under permission from the Ministry of Culture and Tourism, a submerged archaeology research project was launched on behalf of Uludağ University. The primary objectives during this period were to document the current condition of the remains, produce plans and profiles, and determine the preservation conditions of the structure on the lakebed. A floating platform was established on the lake; divers observed wall traces, architectural blocks, and cultural deposits surrounding the structure. Combined underwater photographic and video recordings with measurements enabled the formulation of the building’s general plan layout, and for the first time, wall thicknesses as well as the nave, apse, pastophoria, and narthex-atrium arrangement were documented in detail.

The 2015 season is marked as the beginning of systematic underwater excavations on the structure. During this phase, controlled removal of sediment from the lakebed, stratigraphic excavation in selected trenches, and limited-depth probing especially within the nave and around the apse yielded the first archaeological stratigraphic data. These investigations enabled the basilica to be examined not only at the plan level but also in terms of its phases of use; the recovery of coins, ceramics, and various small finds alongside architectural remains provided the foundation for discussions on the building’s chronology.

The 2016 season was characterized by an expansion in both scope and intensity of underwater excavations. Excavation reports from this season indicate the emergence of necropolis-related data in trenches opened in the naos and adjacent areas. A series of brick tombs were identified adjacent to and aligned with the southern wall of the nave; these tombs were numbered KM-01, KM-02, KM-03, etc. The excavation and documentation of these tombs revealed that the basilica served not only as a church but also as a burial site, demonstrating that interior space and cemetery usage were integrated within a single architectural whole.

In subsequent years (2017 and 2018), underwater excavation and documentation efforts continued with new trenches opened both within the naos and around the apse and pastophoria. Reports indicate that findings such as the exposure of stylobate lines demarcating the nave, identification of in situ column bases, and documentation of parapet slabs and opus sectile floor fragments clarified the building’s architectural design. During this period, observations regarding wall construction, floor paving, and tomb typologies began to accumulate, pointing to distinct phases of construction and use.

During the 2019 and 2020 seasons, intensive work was carried out in a specific trench designated as 12A, located particularly in the northeastern sector of the basilica. Sediment on the lakebed was systematically removed using centrifugal pumps and sieving units down to elevations between –1.27 and –1.57 meters; during this process, a large quantity of wooden fragments, nails, various metal objects, bronze coins, and ceramic sherds were recovered. In the same trench, the discovery of human skull fragments beneath a stone fill suggested that the area continued to be used for burial or secondary purposes in later periods.

The report on the 2021 season marks a new phase in the excavation history. With permission granted by the General Directorate of Cultural Heritage and Museums of the Ministry of Culture and Tourism on 18.05.2021, the excavation directorship was assumed by the Nicaea Museum Directorate, under the responsibility of Ahmet Türkmenoğlu and museum specialist Nazan Canverdi, with scientific support from Uludağ University in Bursa. The team included not only underwater archaeologists but also researchers from other disciplines, such as anthropologist Dr. Songül Alparslan-Rodenberg, endowing the excavation with an interdisciplinary character, particularly in the evaluation of anthropological and biological data. During this season, depth investigations continued in previously identified trenches, and wooden elements and associated finds from tombs were documented.

Overall, each excavation season since the 2014 discovery and preliminary documentation has highlighted a different aspect of the structure. In the early years, the focus was on establishing the plan layout and recording architectural remains; during the 2015 and 2016 seasons, internal burial practices and the necropolis area came to the fore; and in the 2019–2020 and 2021 seasons, deeper trenches revealed a complex history of use represented by wooden elements, metal objects, and human remains. Thus, the structure has been documented both as an early Christian basilica and as a submerged archaeological site characterized by long-term use along the lakeshore and subsequent processes within the lacustrine environment.

Morphological Definition and Plan Layout

The Nicaea Lake Basilica features a three-aisled basilican church plan oriented east-west. The central structure, as preserved in its remains, measures approximately 41.32 meters in length and 18.61 meters in width from exterior to exterior. The central nave is 20.03 meters long and 7.95 meters wide. The north aisle is approximately 3.32 meters wide, while the south aisle is 3.15 meters wide, indicating that the south aisle was slightly narrower than the north. Wall thicknesses average around one meter.

To the east of the naos, there is a main apse with a circular interior plan and a polygonal exterior wall. The diameter of the apse is approximately 6.85 meters. On either side of the main apse are pastophoria chambers; the width of the southern chamber is recorded as approximately 4.06 meters. Initial assessments identified this space as a diaconicon, but excavations in 2017 revealed the presence of a secondary apse within it. Within the southern pastophorion, a sarcophagus measuring 1.97 meters in length and 0.70 meters in width was found adjacent to the southern wall. Thus, at the eastern end, liturgical or monumental arrangements are evident not only in the main apse but also in the lateral spaces.

To the west of the naos, a narthex and, in front of it, a three-unit atrium are arranged sequentially toward the western facade of the structure. The southern wall of the atrium is set slightly inward compared to the narthex wall. This arrangement produces a western facade with both a three-unit courtyard composition and a more dynamic design due to the recessed wall line on the south side. The three-unit configuration of the atrium indicates a central axis emphasized with lateral sections functioning as entrance and circulation areas; the sequential placement of the narthex and atrium creates a multi-layered entrance system on the basilica’s western facade.

In the interior space, the division of the nave was achieved through stylobates and the rows of columns rising upon them. Excavation work conducted at the western end of the north stylobate of the church has yielded detailed information regarding the load-bearing system defining the nave division. Upon removal of the rubble fill, the stylobate plane was revealed at approximately +476 elevation; four Attica Type B column bases were identified at the upper elevation of +506 on the stylobate. It is evident that the spaces between the column bases were later closed off with a rubble stone wall. The plaques, their bases, and upper fragments recovered from this area indicate that high parapet plaques were employed in the nave division, and that the boundaries of the nave were emphasized not only by the rows of columns but also by vertical surfaces.

Two distinct types of column capitals have been identified among the capitals: Corinthian and Ionic–impost. The use of different capital types within the same structure suggests that different load-bearing elements were preferred in the lower level and the possible gallery level. The establishment of the nave division with a “high” arrangement parallels solutions known in early Byzantine churches in terms of both visual permeability between spaces and the structural conception of the upper levels. On the north and south sides of the stylobate, at an elevation of approximately +469, white limestone claddings were detected; these claddings form part of the high-quality flooring material used on the nave floors.

Opus sectile pavements emerge as a significant architectural feature within the structure. In certain areas, a geometric arrangement has been identified, consisting of large sectile pieces placed diagonally at the corners and smaller square and triangular fragments filling the intervening spaces. This arrangement, particularly in sections near the naos and the nave division, can be interpreted as floor designs that reinforce spatial hierarchy. During excavation and documentation, these opus sectile pavements were recorded using a 3D laser scanner, after which their surfaces were covered with geotextile and a thin layer of sand for protection.

Overall, the architectural design of the Lake İznik Basilica is defined by a three-nave basilical plan, a circular interior plan with a polygonal apse on the east, lateral pastophoria rooms, a nartex–atrium complex on the west, stylobates and column rows for the nave division, high parapet plaques, the use of two distinct types of column capitals, and rich opus sectile pavements. These architectural features demonstrate that the building re-creates a classical basilical church schema within the specific topography of the Lake İznik shoreline, both in its scale and in its detailed interior organization.

Construction Phases and Chronology

The area where the Lake İznik Basilica is located does not appear as a narrow plot reserved solely for the construction of a church, but rather as a broad cultural layer containing superimposed traces of settlement and use from multiple periods. Excavation boreholes conducted underwater have revealed both architectural remains and assemblages of ceramics, coins, and small finds, enabling the chronological sequence of the site to be traced in several main phases.

Pre-Basilica Use

The earliest finds, located beneath and around the basilica’s architectural remains on the lakebed, indicate that the area had been in use since the Late Hellenistic and Early Roman periods. In particular, borehole 12A, excavated in the atrium section, yielded data dating to the 1st century BCE at a depth of approximately –1.97 meters. The discovery of a bronze coin struck in Prusa ad Olympum in honor of C. Papirius Carbo, proconsul of Bithynia–Pontus, suggests that this area along the lakeshore was in use no later than around 62–59 BCE. Late Hellenistic ceramic fragments found at the same level confirm that this dating is not coincidental and point to a continuous function in this sector from the 1st century BCE onward.

Although no complete architectural plan from this early phase has yet been identified, the coins and ceramics reveal that the lakeshore was utilized as a site connected to urban activity. It remains unclear whether the area served as a dock, warehouse, workshop, or another function during this period; however, the density of Hellenistic–Roman finds demonstrates that the location of the basilica had previously been part of a coastal zone integrated into the daily life of the city.

First Construction Phase: Late Antiquity

The earliest evidence pertaining to the basilica itself emerges from the combined analysis of architectural features and coins dated to the late 4th and early 5th centuries. The three-nave plan, the circular interior with a polygonal apse, lateral rooms adjacent to the apse on the east, and the nartex–atrium sequence on the west are consistent with the classical basilical church typology of Late Antiquity. The column bases, parapet plaques, and opus sectile arrangements on the floors indicate a date within the 4th–5th century range, both in terms of architectural form and decorative program.

Coins found within the naos and particularly in layers associated with burials include examples dating to the reign of Emperor Valens (364–378 CE), indicating that the church was in use no later than the second half of the 4th century. When considered together with the architectural features, these data suggest a construction timeframe for the basilica between the final quarter of the 4th century and the early 5th century, following the official imperial acceptance of Christianity.

The association of the building with the cult of Saint Neophytos appears chronologically plausible. In Christian tradition, Neophytos, who was martyred at a young age, is said to have been killed near the lakeshore, and a church was later erected in his honor at that site. This narrative supports the placement of the basilica’s initial construction phase within the Late Antique period, when martyr cults became widespread; however, no inscription or documentary evidence directly confirming this connection has yet been identified.

Repairs, Reconfigurations, and Middle Byzantine Phases

Excavations have revealed interventions differing in character from the original masonry, including additional walls constructed with different stonework and bonding materials, as well as closures of previously open spaces. For instance, a wall cutting across the stylobate line defining the nave division was found to have been built in a later phase. The partial filling of the spaces between column bases with rubble stone suggests that the original nave division, defined by open colonnades, was gradually transformed into a more enclosed arrangement in subsequent centuries.

Such interventions demonstrate that the church was not abandoned shortly after its initial use, but rather underwent repairs and reconfigurations across multiple periods. Relationships between wall masonry, floor coverings, and burial placements imply that new liturgical arrangements were introduced and that the functions of certain spaces changed over time. The apse identified in one of the pastophoria rooms indicates that these lateral chambers also became increasingly emphasized liturgically over time.

A detailed century-by-century chronology for these phases has not yet been fully established; however, the analysis of ceramic and coin finds suggests that the church functioned as an active place of worship during the Early Byzantine period (approximately 6th–7th centuries), while its primary function shifted toward burial use in later centuries.

Late Use, Necropolis Function, and Abandonment

Artifacts from the Middle and Late Byzantine periods reveal that the interior space and surrounding areas of the structure were used for an extended period as a cemetery. Brick-vaulted tombs adjacent to the southern wall of the naos, burials extending beneath the bema wall, and the presence of multiple individuals within single graves indicate that the interior of the basilica gradually transformed into an intensive burial zone. A significant proportion of the coins recovered from these tombs date to the 11th–13th centuries.

Metal crosses found in the upper layers, particularly those in the Latin cross form and with hollow interiors designed to hold relics, are consistent with the proposed dating range of the 10th–12th centuries. Such objects are commonly found in Byzantine contexts associated with burials and areas linked to saintly relics. The discovery of a similar cross at the Lake İznik Basilica suggests that the building retained associations with sanctity and commemorative significance during its later phases.

Upper fill layers composed of irregular stone piles, broken architectural blocks, and disordered human remains indicate that planned use of the structure gradually declined in its final phases. The earthquake of the 8th century, known to have severely affected Nicaea, is frequently cited in the literature as the primary event linked to the submergence of the basilica beneath lake waters. When considered together with tectonic activity along the lakeshore, fluctuations in water levels, and earthquake-induced subsidence, the collapse and submergence of the structure can be explained as the result of multiple geological events.

The filling characteristics observed in the atrium area and around the church suggest that the structure was not simply left to collapse naturally, but rather underwent a degree of controlled burial. Particularly above levels containing late medieval coins and relic crosses, the presence of large stone fragments and a compact fill layer is interpreted as evidence that the area was eventually sealed from above alongside its use as a cemetery.

At the depth reached by the underwater excavations, the chronology of the Lake Iznik Basilica can be outlined within the following general framework: initial use along the lakeshore beginning in the 1st century BCE and continuing through the Roman period; construction of a three-aisled basilica during the Late Antiquity and its function as a place of worship in the Early Byzantine era; followed by an increasingly intensive necropolis function during the Middle and Late Byzantine centuries, culminating in the structure’s collapse into the lake environment and its partial deliberate covering by fill material before abandonment. This timeline remains open to further refinement through future excavations and analyses.

Liturgical Layout and Religious Function

The architecture of the Lake Iznik Basilica reflects a design concept that prioritized liturgical function from the outset. The three-aisled arrangement along the east-west axis, with an apse and adjacent side chambers to the east and a narthex and atrium sequence to the west, suggests a clear spatial demarcation between the congregation and the clergy. This layout establishes an order that guides movement and transition during worship while emphasizing the hierarchy between the sacred space and the congregational area.

The apse at the eastern end of the naos is the most privileged area liturgically. Its circular interior structure, containing the bema, likely served as the sacred space where the altar stood and the clergy gathered. The bema wall separating the apse from the nave and the parapet slabs identified along the nave boundaries indicate that during worship, the clergy and congregation were physically and visually separated to a measurable degree. When considered together, the column bases, parapet fragments, and floor pavings reveal that the eastern end was not a freely accessible area for ordinary congregants, but rather a space reserved for clergy performing specific liturgical duties.

The side chambers flanking the apse evoke the typical arrangement of diakonikon and prothesis rooms found in early Christian churches. The discovery of a small apse and a built-in tomb adjacent to the southern pastophorion suggests that this space was not merely a service area but may also have functioned as a monumental sacred chamber. The presence of the tomb strengthens the impression that this space was associated with the relics of a saint or a locally venerated individual; in such a case, the chamber would have served both as a site for liturgical preparations and for commemorative rituals.

The generous width of the central nave is decisive in determining the congregation’s positioning during worship. The broad central nave emphasizes the main axis extending from the entrance to the apse and creates a central focal point where the congregation gathered during services. The side aisles were likely used for more controlled movement, circulation, and secondary functions. The opus sectile pavements identified on the nave floors are regarded as elements that enhanced the visual impact of areas considered especially significant liturgically; these geometrically patterned floors elevated the spatial representation of the church and provided a symbolic backdrop distinguishing the sacred space from mundane environments.

The sequential arrangement of the narthex and the three-part atrium at the western end of the building indicates a graduated transition scheme liturgically. The atrium may have functioned as a gathering space for the congregation before entering the church, a venue for ceremonial processions on specific days, or a waiting area for catechumens prior to baptism. The narthex, positioned as the final threshold before the main worship space, facilitated the orderly entry of worshippers and served as an intermediate zone for those partially participating in the liturgy according to ecclesiastical discipline. Thus, the internal organization of this church along the lakeshore, progressing from west to east, reflects a staged transition from the secular realm to the sacred.

The relationship between the interior space of the basilica and burial practices is also crucial for understanding its liturgical function. Within the naos, particularly along the southern wall and extending up to the base of the bema wall, brick-vaulted tombs indicate that the worship area also functioned as a necropolis. Tombs located near the bema and apse suggest that the interred individuals held a status distinct from other congregants; such burials in the Byzantine world were typically reserved for clergy, local elites, or individuals associated with saint cults. The coexistence of worship and burial within the same space reveals a practice that integrated liturgical ritual with commemorative veneration.

Written and oral traditions associate the building with Saint Neophytos, raising the possibility that the basilica served as a martyrion. In a church believed to have been constructed in memory of a saint martyred at the lakeshore, one might expect large congregations to gather along the shore during feast days dedicated to the saint, commemorative rites to be held at the site linked to his tomb or relics, and processions carrying icons and relics. Although not directly supported by inscriptions, the cross-shaped objects and fragments interpreted as containers for relics recovered during underwater excavations imply that the space continued to function as a significant devotional center connected to a saint cult.

When evaluated together, these findings reveal that the liturgical layout of the Lake Iznik Basilica—defined by the sacred area of the apse and bema, the possible service and commemorative functions of the pastophoria chambers, the nave sections designated for the congregation, and the western narthex–atrium sequence—uncovers the internal organization of an urban sacred site on the lakeshore. The building occupies a critical position in Iznik’s Christian-era religious topography, functioning simultaneously as a church for regular worship, an integrated burial ground, and a probable center of saint veneration.

Necropolis and Burial Practices

The underwater excavations at the Lake Iznik Basilica reveal that the structure was not only used as a place of worship but also as a long-term burial site. Particularly within the naos, concentrations of tombs along the southern wall and near the bema constitute a clear example of the practice of in-church burial. A significant portion of these tombs date to periods later than the basilica’s initial phase of use, specifically to the Middle and Late Byzantine centuries; this suggests that even as its liturgical function continued or declined, the building transformed into a monumental cemetery area that retained its symbolic significance.

Adjacent to the south wall of the naos, a row of tile-roofed graves arranged side by side constitutes one of the most densely concentrated burial areas. These rectangular graves were constructed by surrounding the body with tiles, filling the interior with earth, and covering the top with another layer of tiles. During excavation, these graves were designated with codes such as KM-01, KM-02, and KM-03; in some cases, skeletal remains belonging to multiple individuals were found within a single grave. This indicates that the graves were reopened over time and reused for family or group burials, demonstrating that the same location was preferred for multiple interments.

Some burials located very close to the bema wall are significant in terms of the hierarchical structure within the church. Proximity to the altar and apse in Byzantine burial tradition is typically associated with individuals of high ecclesiastical status or local elites. The arrangement and positioning of graves near the bema line in the Basilica of Lake İznik suggest that those buried there may have held a different social standing compared to other grave occupants. Similarly, a sarcophagus discovered in one of the pastophoria rooms stands out as a possible special burial associated directly with a saint or a venerated individual; such graves imply that the space functioned not merely as a common burial area but as a monumental and commemorative focal point.

The grave typology reveals the diversity of burial customs. In addition to tile-roofed graves, burials arranged as stone sarcophagi, sarcophagi, and simpler secondary burials defined by fill material have also been identified. While some graves preserve primary burial arrangements with articulated skeletons, others show bones gathered together, indicating secondary reorganizations following earlier interments. This pattern demonstrates that those buried within the church were not confined to a single period but reflect a long-term, multi-century use of the site as a cemetery.

Anthropological analyses assist in understanding not only the numerical distribution of graves but also the demographic characteristics of the interred individuals. The presence of child burials alongside adult remains in some graves suggests that the church served as a burial ground for a broad segment of the community rather than a specific social group. Although details regarding sex and age distribution are limited by the preservation state of the skeletons, the co-burial of individuals from different age groups within the same spatial context reinforces the impression that the churchyard was used on a familial or communal basis.

Artifacts recovered from the graves provide additional insights into burial rituals. In some burials, bronze or copper coins, small cross-shaped objects, simple jewelry pieces, and occasionally glass beads or pellets have been identified. Coins not only help narrow the chronological range of the burials but also confirm the practice of placing currency in graves as part of funerary rites. Cross-shaped objects and crosses likely used for relic transport can be interpreted as clear indicators of Christian identity in the burials. The rarity of rich or ornate grave goods suggests that the site functioned not as a “prestige necropolis” but as an urban parish cemetery.

The orientation of the graves is another notable feature. In many graves within the church, the heads were typically positioned along a west–east axis, with the faces oriented toward the east. This orientation reflects a widespread practice in the Byzantine world associated with the belief in resurrection; since the east was symbolically regarded as the direction of Christ’s return in liturgical and theological contexts, burying the deceased with their faces turned eastward carried significant symbolic meaning.

The use of the basilica as a necropolis progressed alongside its abandonment. Irregular stone piles, mixed bone fragments, and coins from later periods found in upper fill layers indicate that the cemetery layout was disrupted over time, with some graves reopened and the burial area subjected to later interventions. Particularly, the nature of the fill around the atrium reveals that scattered burials or displaced skeletal fragments may also have existed in the immediate vicinity of the building; this suggests that not only the interior space but also the surrounding area was utilized as a burial ground.

Small Finds and Material Culture

The small finds recovered from the Basilica of Lake İznik demonstrate that the site possessed a multifaceted character not only architecturally but also in terms of daily life, worship practices, and long-term use. Ceramics, coins, glass and metal objects, and liturgically significant small artifacts contribute to refining the chronology and understanding the evolving functions of the site across different phases.

Ceramic Finds

Ceramic artifacts constitute the largest group of finds from excavation and survey work. Ceramics recovered from various contexts vary in manufacturing techniques, fabric composition, glaze, and decoration types, reflecting a broad chronological span from the Late Hellenistic to the Middle–Late Byzantine periods.

In early layers, particularly in the atrium and lower levels of the building, fragments of tableware and storage vessels dating to the Late Hellenistic and Early Roman periods are prominent. These vessels, characterized by thick walls and often reddish or light brown fabrics, indicate that the area along the lake shore was in use prior to the construction of the basilica and supported daily activities. This group includes vessels with smoothed interiors and simple forms, as well as fragments with ribbed bodies and profiled rims.

During the Late Antique and Early Byzantine phases, when the basilica was constructed and actively used as a place of worship, more refined tableware, cooking vessels, and lamps become prominent. Thin-walled, well-fired pieces, often with red slips and occasional incised or relief decoration, reflect the table culture of this period. Some examples exhibit internal smoothing and simple geometric ornamentation. Alongside everyday vessels, fragments of oil lamps provide evidence for the church’s lighting system; examples bearing cross motifs and simple symbols on the handle and disc areas can be directly linked to Christian iconography.

In upper layers associated with the Middle and Late Byzantine periods, the proportion of glazed ceramics increases. Glazed fragments in green, yellow, and brown tones, with fine slip surfaces and combined incised-painted decoration techniques, represent typical examples of the Byzantine ceramic repertoire of this era. These vessels are found mixed within graves and surrounding layers, possibly serving as grave offerings, everyday utensils, or fill material during the centuries when the basilica was intensively used as a necropolis.

Coin Finds

Coin finds constitute the most important group of small artifacts for establishing the chronology of the basilica and distinguishing its phases of use. Coins recovered from various contexts provide a chronological sequence documenting both the pre-basilica Hellenistic–Roman usage and the functioning of the basilica during the Late Antique and Byzantine periods.

At lower levels, particularly in boreholes within the atrium area, bronze coins dating to the 1st century BCE have been identified. These examples associated with the Bithynia–Pontus provincial administration indicate that the lakeshore area was actively used during both the pre-Roman and early Roman periods. When evaluated alongside ceramic data, these findings support the interpretation that the shoreline strip was an integral part of urban activity prior to the construction of the basilica.

Strata associated with the construction phase and early use of the basilica yield coins dated to the late 4th and early 5th centuries. Bronze coins from the reigns of Emperor Valens and his successors suggest that the church was operational during these centuries. Most of these coins were recovered from within the naos and around the apse, sometimes in association with burials; this indicates that burial activities were present from the earliest stages alongside the religious use of the space.

At upper levels, particularly within the fill layers of graves in the naos, Byzantine coins dating to the 10th–13th centuries are found. Some of these late-period coins occur in burial contexts while others are found mixed within fill deposits. Examples of coins placed alongside the deceased in graves point to the continuation of classical Christian burial rituals. At the same time, these late coins demonstrate that the basilica was used for an extended period as a necropolis and that the site remained visited long before it became submerged.

Glass and Metal Objects

Although glass finds are numerically more limited compared to ceramics and coins, they provide significant information regarding usage patterns. Fragments of glass vessels recovered from various excavations include thin-walled drinking vessels, small bottles and bowls, as well as components of lighting devices. Slight thickening along the edges and body junctions of some glass fragments suggests the presence of hanging or footed lamp types. The color of the glass is predominantly greenish or bluish tones, consistent with early Byzantine production characteristics.

Metal finds exhibit a broader range of types. Bronze and iron nails, various-sized fasteners, and structural elements reflect traces of both wooden superstructures and construction components that have since deteriorated in the lacustrine environment. Particularly dense concentrations of nails and metal fragments in excavation area 12A suggest extensive use of wood in the upper structure and indicate that these wooden elements were preserved for long periods within the sediment at the lakebed.

Among metal objects of daily use are simple brooches, small rings and hooks, and probable belt or clothing accessories. Some of these items were found in burial contexts, others within mixed fill deposits. Metal jewelry fragments discovered in graves suggest that personal belongings were buried with the deceased; however, the rarity of elaborate, high-craftsmanship metal objects points to a relatively modest material culture consistent with the overall character of the site.

Special Liturgical Objects

Some small finds from the Basilica of Lake Iznik can be directly linked to liturgical functions and the cult of saints. These include cross-shaped objects and reliquary components. One of the most striking discoveries is a bronze cross of Latin form, featuring a hollow interior compartment and designed in two parts. Such crosses, with hollow bodies and lid-like closures, were commonly used in the Byzantine world to carry protective relics or small holy fragments.

The discovery of such a reliquary cross within the church, in a location connected to a grave or sacred area, supports interpretations linking the building to saint veneration. When considered alongside the traditional narrative associating the site with Saint Neophytos, these liturgical objects suggest that the basilica was not merely a local parish church but also a sacred site with martyr-related significance.

The liturgical assemblage also includes smaller crosses, simple decorative crosses, and probable metal accessories used during worship. Some of these items were likely used directly in liturgical practice, while others may have functioned as jewelry or personal protective objects. The presence of the cross motif on ceramic lamps and stone/plastic fragments further demonstrates the clear reflection of Christian symbolism within the material culture of the building.

Overall, the small finds materially reflect the historical transformations of the Basilica of Lake Iznik: Hellenistic–Roman vessels and coins attest to early lakeshore use; late antique and early Byzantine ceramics and coins document the construction and liturgical phase of the basilica; while medieval and late Byzantine coins, glazed vessels, and grave goods represent the period when its function as a necropolis became dominant.

Iznik City, the History of Christianity, and Regional Context

Historical Development of Iznik and Lakeshore Settlement

The area where the Basilica of Lake Iznik is located represents a shoreline zone immediately outside the ancient city walls of Nicaea facing the lake. The section of the city walls bordering the lake had a gentler topography compared to the landward walls; this lakeside boundary became one of the city’s outward-facing fronts, serving both defensive and transport functions. The basilica’s position approximately 50 meters offshore suggests that at the time of its construction, the structure was designed as a land-based edifice directly adjacent to the lakeshore, and its current submerged state is the result of later geomorphological processes.

Nicaea became one of the region’s major cities from the Hellenistic period onward. During the Roman Empire, it developed administratively and economically, functioning as a regional center with its wall system, main streets, and public buildings. During this period, the lakeshore was likely equipped with small-scale piers, storage facilities, and areas dedicated to water-related activities. The line on which the basilica stands lies along an outer band parallel to the lake-facing section of the city walls; this band served as a transitional zone connecting the urban core with the water and accommodating extramural sacred structures and cemeteries.

During the late antique and Byzantine periods, the interior fabric of Nicaea acquired a new religious topography with the rise of Christianity; churches, chapels, and martyr shrines became concentrated within and near the city walls. The basilica on the lakeshore became part of this new topography. Its orientation toward both the city and the lake suggests it was situated at a point where land routes intersected with probable water routes; thus, the basilica formed a sacred focal point connected not only to urban circulation but also to movement across and toward the lake.

During the Ottoman period, İznik assumed a settlement character dominated by Islamic identity; new religious building types (mosques, small mosques) came to dominate the urban fabric. During this period, early Christian structures along the lake shore were largely erased from the surface, while the Basilica of Lake İznik continued to exist as a submerged cultural layer beneath the lakebed. Underwater excavations have made visible the archaeological traces of this prolonged transformation process through architectural remains and stratigraphic deposits.

Christian History and İznik

Nicaea became one of the cities of imperial significance in early Christian history. The councils held in the city and its episcopal organization elevated Nicaea beyond the status of a local center, transforming it into a focal point for theological debates and church administration. In this context, churches and other Christian structures in İznik were not merely places of worship for local congregations but also served as venues through which decisions and doctrinal currents accepted at the imperial level were disseminated.

The Basilica of Lake İznik constitutes a unique example within this broader Christian topography, situated directly along the lakeshore. Its traditional association with Saint Neophytos, who was believed to have been martyred at a young age, elevated the basilica beyond the role of a city church to that of a sacred site imbued with martyrdom. Considering the relationship between martyr cults and urban topography during the early Christian and early Byzantine periods, the construction of such a structure along the lake shore reflects a tangible manifestation of the connection between saint veneration and urban space in Nicaea.

When evaluated alongside other churches and monastic structures in the city, the exact hierarchical status of the Basilica of Lake İznik within the Nicaean episcopal organization remains undetermined today; however, its architectural scale, interior layout, and necropolis function suggest that it may have served not just a narrow congregational group but a broader urban population. The high density of burials within the church, evidence of long-term use, and liturgical objects indicate that this lakeshore structure may have functioned as a central site for both worship and commemorative practices during the Christian period in İznik.

Regional and Imperial Evaluation

The Basilica of Lake İznik largely conforms to the tri-aisled basilica typology widely used in Anatolia and the Eastern Mediterranean during the Late Antique and early Byzantine periods. The east-west oriented three-aisle plan features, on the eastern end, an apse with a semicircular interior, flanking pastophoria chambers, and on the western end, a narthex preceded by an atrium—constituting the fundamental elements of this shared architectural schema. The use of column rows, parapet slabs, and richly decorated floor pavements reflects an internal spatial hierarchy consistent with that observed in contemporary churches.

Nevertheless, the basilica’s direct location along the lakeshore and its current submersion beneath the water distinguish it among regional examples. Although churches built along coasts or lake margins in Anatolia are known, the preservation of a basilica of this scale underwater renders the Basilica of Lake İznik a unique case in both underwater archaeology and the study of sacred structures in relation to shoreline topography. The basilica’s intact architectural form, preserved on the lakebed to the present day, has contributed valuable underwater data to regional basilica typology studies.

From a regional perspective, the Basilica of Lake İznik must be assessed in relation to other early Christian centers in Bithynia and its surroundings. The cities, episcopal networks, rural churches, and monastic complexes of the region, together with numerous contemporaneous structures, formed a Christian geographical landscape. İznik occupied a central position within this network; the basilica on the lakeshore stands as one of the physical manifestations of the city’s strategic location.

From an imperial perspective, the chronological and architectural data obtained from the Basilica of Lake İznik reveal how martyr cults, urban necropolises, and lakeside settlements underwent transformation from the Late Antique period through the Middle Byzantine era. In its early phase, emphasis was placed on worship and martyrdom; in subsequent centuries, its function as a necropolis intensified; and in its final phase, it became a preserved cultural layer beneath the lakebed due to geomorphological processes and seismic effects. Thus, the Basilica of Lake İznik serves both as a concrete embodiment of Nicaea’s role in Christian history and as a research area where coastal and underwater archaeology are jointly examined, becoming an important source of data for regional and imperial-level evaluations.

Conservation, Management, and Underwater Archaeological Methods

Underwater Archaeological Methods

Work conducted at the Basilica of Lake İznik has been carried out from the outset using a methodological framework specifically adapted for underwater archaeology. Floating platforms anchored to the lake surface served both as access points for divers and as operational areas for measurement, documentation, and artifact recovery. This established a controlled working environment relatively independent of daily wave action and shoreline traffic.

Excavation on-site followed a diving-based methodology. Divers were supplied with air via surface-fed snorkel systems, eliminating the need for frequent ascents to change tanks. In the lake environment, where visibility was sometimes limited, divers progressed along defined lines and reference points; excavation units were defined using a grid system tied to a coordinate framework. Each unit was recorded through plan and section drawings accompanied by elevation measurements; underwater measurements were verified using surface-based methods.

The lakebed fill surrounding the basilica was systematically removed using centrifugal pumps connected to hose systems. Divers directed hoses to suction silt and fine sediments from selected excavation units, transporting them to surface screening units. Here, sieves with varying mesh sizes were employed: clay, silt, and finest particles were returned to the water, while ceramic, glass, metal fragments, and small bone pieces were retained on the sieves. This method enabled the systematic recovery of small artifacts that might otherwise have been lost under the lake’s low-visibility conditions.

For the documentation of architectural remains, classical underwater survey techniques were supplemented with photogrammetry and three-dimensional laser scanning. Wall traces, column bases, parapet slabs, sarcophagi, and floor pavements were photographed from multiple angles; these images were then combined in software to generate three-dimensional models. In particular, the immediate three-dimensional recording of opus sectile floors and delicate architectural sculptural elements upon their exposure during excavation has laid the foundation for future reconstruction and virtual visualization efforts.

During excavation seasons, a phased approach was applied to the exposure of human remains to prevent loss of anthropological and biological data. Skeletons were documented in situ without disturbance; after photographic and drawn records were made, they were carefully removed in fragments. During this process, small wooden wedges and baskets were used to prevent bones from shifting or mixing, accounting for the buoyancy of water and sediment movement. Similar care was taken in the identification of wooden artifacts: visible wooden fragments were photographed and drawn after slight removal of surrounding sediment, and those deemed essential were lifted in blocks.

Conservation Issues and Risks

The conservation conditions of the Basilica of Lake İznik are directly linked to the dynamics of the lake ecosystem. Fluctuations in lake level, changes in water temperature, and wave-induced erosion along the shoreline constitute the primary factors exerting long-term pressure on architectural remains. In particular, stone blocks and wall traces near the shore are more severely affected by sediment and sand movement caused by wind-driven surface waves.

Biological activity at the lakebed has also emerged as a significant concern for conservation. Algae, aquatic plants, and shellfish have adhered to both stone surfaces and wooden and metal artifacts. Over time, the thickening biological layer has made it difficult to read surface details and, in some cases, has created microenvironments that accelerate the deterioration of stone surfaces. Consequently, during excavation seasons, areas with dense biological deposits were identified, and limited, controlled cleaning operations were carried out where necessary.

Human-induced risks have also been taken into account. Recreational use of Lake İznik, fishing activities, and unregulated diving attempts have been identified as potential threats to the integrity of the remains. Fishing nets and lead weights becoming entangled in architectural blocks may have caused stones to shift or fracture. Therefore, the excavation area was enclosed within a designated safety buffer; its coordinates were officially recorded by authorities, and measures were taken to restrict unauthorized activities.

The preservation of small artifacts is closely linked to the interventions applied after their removal from the underwater environment. Ceramic and glass fragments were dried in a controlled manner to prevent cracking caused by rapid desiccation upon removal from water. Metal artifacts, particularly bronze and iron pieces, were first stored in solutions with conductivity similar to that of the lake water to prevent sudden oxidative reactions with oxygen upon exposure; they were then subjected to mechanical and chemical cleaning procedures by specialist conservators. Wooden fragments were transferred to temporary storage environments designed to maintain their water-saturated state, thereby minimizing volume loss and deformation.

Display, Visitor Management and Museumization

The conservation of the Basilica of Nicaea has not been limited to excavation and conservation techniques; considerable discussion has also focused on how the site should be presented to the public and how visitors should be engaged. Opening the underwater remains directly to underwater tourism would have required extreme caution regarding both safety and preservation. Therefore, an approach was adopted that treats the area surrounding the structure as a controlled underwater archaeological zone, accessible only to trained divers and research teams along designated routes.

Presenting information about the site on land has emerged as a method that balances conservation with public outreach. Through panels and visual narratives placed near the lakeshore, visitors have been provided with the basilica’s plan, photographs, and three-dimensional models. This approach ensures that the remains remain undisturbed underwater, while informative content about the structure becomes accessible on land. Three-dimensional photogrammetry and laser scanning data have generated high-quality visual materials suitable for both scholarly publications and museum exhibitions.

Portable artifacts recovered during underwater excavations have been transferred to the museum in accordance with relevant legislation and incorporated into the museum’s collection. Ceramic groups, coins, glass and metal fragments, and liturgical objects have been classified according to typological and chronological criteria and arranged thematically both in storage and in exhibition halls. Thus, a functional division of responsibilities has been established between the architectural remains preserved in situ at the lakebed and the portable artifacts: the architectural structure remains in the lake, while smaller artifact groups are presented to visitors in the museum environment.

In the long term, the proposed conservation and management approach for the Basilica of Nicaea is based on preserving the structure in situ, rejecting alternatives such as physical relocation or reconstruction. Instead, the method emphasizes in-place conservation and the digital presentation of documented data. Plans, cross-sections, photographs, and three-dimensional models obtained during underwater excavations form the foundational material for both scientific research and public outreach initiatives. In this way, an equilibrium between the lake’s ecosystem and the archaeological heritage has been sought, and the Basilica of Nicaea is treated as a documented and managed cultural asset within its underwater conditions.