Karaköy Underground Mosque

Karaköy Underground Mosque is a historic mosque located in the Beyoğlu district of Istanbul, adjacent to the Karaköy steamship pier close at place site. Notably distinguished by its architecture and history, this mosque is unique among Istanbul’s mosques as it was constructed underground. The Underground Mosque is one of the religious structures of both Istanbul and the Ottoman Empire, standing out both as a place of worship and for its historical and cultural significance.

Underground Mosque (Source: Geographical Travels)

History and Transformation

The site of the Karaköy Underground Mosque was originally part of the Byzantine-era Galata Castle (Kastellion), built to block ship access to the Golden Horn. It is known that this structure served as one end of the chain stretched across the Golden Horn during the siege of Constantinople. After the Ottoman conquest, the structure continued to be used for various purposes by the Ottoman Empire, including as a warehouse, armory and water cistern like>.

In the 17th century, Nakşibendi scholar Mehmet Efendi had a vision in which he saw the Companions of the Prophet in this area. As a result, it was discovered that the vault contained the graves of these Companions. This discovery laid the foundation for the construction of the mosque. In the 1750s, under the initiative of Köse Bahir Mustafa, grand vizier of I. Mahmud, work began to convert the vault into a mosque by placing the Companions’ graves inside. Thus, between 1753 and 1756, the Karaköy Underground Mosque was officially opened for worship.

Architectural Structure

The Karaköy Underground Mosque has a rectangle plan and consists of 54 thick supporting piers upon which barrel vaults are constructed. These vaults are supported by semi-domes covering the upper part of the structure. Unlike other mosques, the interior space is illuminated not by natural light but solely by light entering through the sea walls. The interior contains numerous historical and religious elements, including the graves of the Companions. Access to the mosque is possible from two directions: one from the Karaköy pier side, and the other via stairs at the end of a dead-end street reachable from Karaköy Square. Upon first entering the mosque, visitors encounter a low-ceilinged and dim atmosphere rather than the traditional high-domed mosques. This difference reflects the building’s underground location.

Underground Mosque. (Source: https://edition.cnn.com/travel/ancient-secret-places-hidden-under-turkey/index.html)

Graves of the Companions

The mosque also holds significant religious importance due to the graves of the Companions it houses. Within the structure are the tombs of Companions such as Amr ibn al-As, Wahb ibn Husayra and Sufyan ibn Uyayna, who participated in the siege of Constantinople during the Umayyad period. These tombs were marked and protected with coffins during the reign of I. Mahmud. One of the mosque’s most notable features is that the individuals buried here were Companions who died as martyrs during the siege of Constantinople.

Graves of the Companions (Source: Source: Morning)

Use Through Time

The Karaköy Underground Mosque is not merely a place of worship but also a religious center that has attracted numerous visitors to Istanbul. In 1932, it became historically notable as the site where the first Turkish Law'a-ı Kerim was recited. The mosque is also among the most visited religious sites in Istanbul after the Sultanahmet Mosque.

Current Status

Today Karaköy Underground Mosque continues to function as an active place of worship. Above the mosque stands a structure from the Ottoman period known as the Kurşunlu Köşk building. The mosque was restored in 1985, with its original architectural elements preserved and maintained to the present day. Alongside the Karaköy Ferry and surrounding significant structures, the mosque forms an essential part of Istanbul’s historical fabric. Visitors come here both for spiritual reasons and to bear witness to Istanbul’s history. The Karaköy Underground Mosque is a structure that has assumed various functions and evolved through different dynamics throughout history. With both secular and religious depth, this mosque offers a unique experience distinct from other mosques in Istanbul, thanks to the special character imparted by its underground construction atmosphere.