Fort of Galata

The Fort of Galata, now known as the “Underground Mosque” (Turkish Yeraltı Camii), was an important fortification in the region of Galata. It is a multi-layered structure that provides a continuous link from the Byzantine and Ottoman periods to the present. From a typical early Byzantine defensive structure to a bastion arsenal on the Genoese fortifications, the building functioned as the northern corner of the legendary chain closing off the Golden Horn. In the Ottoman period, as the site maintained its position as the maritime corner of Galata at the entrance of the port, the edifice was consequently converted to multiple forms and functions, serving as a granary, customhouse, imperial kiosk and finally a mosque.
Both archaeological evidence and tradition favor the identification of the raised substructure of the Underground Mosque with the foundations of the Fort of Galata. While it is now about 50 meters inland, it originally would have been located by the shore. Preserved as the prayer hall of the mosque, the undercroft (155 x 170 cm) is formed of bays spanned by identical low groin vaults resting on large piers. Today 42 piers are visible, though it originally had as many as 63.
It seems that the Subterranean Mosque was once the foundations of a fort (kastellion) in Galata, which served as a point of attachment for this chain that barred the mouth of the Golden Horn. The chain went from Galata to the Tower of Kentenarion near the Acropolis. The foundation date of the Fort of Galata is not precisely known. The first reference to this fort - and to chain closing off the Golden Horn – appears in accounts of the Second Arab Siege of Constantinople (717-718). While it is possible that the Fort of Galata had towers before the Genoese period, it is clear that it had towers by the time the Genoese controlled Galata.

The Fort of Galata played a key role in the Fourth Crusade and the conquest of Constantinople in 1204. The naval assault, led by the Venetians, did not attempt to attack the Byzantine ships ranged behind the chain drawn across the mouth of the Golden Horn to defend it, but rather the Crusaders chose to attack the Tower of Galata on the northern side of the Golden Horn, where the chain came ashore, and thus to break the chain that way. Once the chain was broken, the Venetians quickly overcame what remained of Byzantine naval forces were in the Golden Horn – forever ending of glory of the Byzantine navy and its dromon.
In 1261, the Byzantine emperor Michael VIII Palaiologos (1259-1282) managed to win back Constantinople. In restoring trade concessions with Italian merchants, Michael VIII preferred to settle the Genoese at the north of the Golden Horn at Galata. It seems that much of the fortifications of Galata were demolished before the region was given over as a concession to the Genoese, though the Byzantines kept the Fort of Galata in order to defend the Golden Horn. It seems that the Fort of Galata was left free-standing however it still preserved its function as a Byzantine military base guarding the entrance of the Golden Horn and as the bridgehead of the chain. After the 1310s the Genoese began constructing their own fortifications. The Genoese referred to the fort as the “Castle of Holy Cross” and as early as 1420 it already started functioning as the arsenal, probably a magazine of guns and gunpowder, as well as the storage of the chain. These transformations continued until the free-standing fort became a fortified tower linked to the rest of the Genoese walls of Galata.

When the Ottomans captured Constantinople in 1453, the Genoese also surrendered Galata. The Fort of Galata, which had been a Byzantine property within the Genoese colony, was taken into the Ottoman imperial ownership. The chain was never used in the Ottoman period, however the bastion retained its late Byzantine usage as a magazine. The building was used as an arsenal for the storage of gunpowder, as it was close to Tophane (the cannon foundries) established by Sultan Mehmed. By the mid 16th century the building, which was transformed into a granary, had a lead roof and subsequently became known as the Leaded Magazine (Turkish Kurşunlu Mahzen). 

During the reign of Mahmud I (1730-1754), the prophecy of a Nakshibendi sheikh from Damascus led to the discovery of the relics of three martyrs in the Umayyad sieges (Vehb bin Huseyre,  Amr bin As and Süfyan bin Uyeyne) in leaded coffins – thus giving new meaning to its name, the Leaded Magazine. This in turn led to the structure being converted into a mosque by the Grand Vizier Mustafa Pasha with the permission of the Sultan in 1752. In 1870s the structure was substantially altered as its frame was in part used in the construction of the Offices of Public Health.

Chain of the Golden Horn at Istanbul Arc

Section of the Golden Horn chain 

Istanbul Archaeological Museums

Depiction of Chain across the Golden Horn

From the Nuremberg Chronicle (1493)

Depiction of the Fort of Galata

From map by Cristoforo Buondelmonte (1422)

Detail of Galata with Fort (top left)

From Map of Constantinople by Piri Reis (1521)

Detail with Leaded Magazine from Panorama of Constantinople by Henry Aston Barker (1817)

British Library

Custom House in Constantinople by Coke Smyth (1838)

Tombs of Vehb bin Huseyre and Amr bin As

Tomb of Süfyan bin Uyeyne

Plan by Mamboury

Map of Galata by Wolfgang Müller-Wiener

Blue indicates location of tower and chain


Urban Palimpsest at Galata & An Architectural Inventory Study for the Genoese Colonial Territories in Asia Minor by Sercan Saglam

“The Corner of the Horn: An Architectural Review of the Leaded Magazine in Galata Istanbul” by Namık Erkal

The Age of the Dromon: The Byzantine Navy ca 500-1204 by Pryor and Jeffreys 

Bildlexikon zur Topographie Istanbuls: Byzantion, Konstantinupolis, Istanbul by Wolfgang Müller-Wiener

Oxford Dictionary of Byzantium edited by Alexander Kazhdan



Galata Album (Byzantine Legacy Flickr)

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Created by David Hendrix Copyright 2016