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Fort of Galata

The Fort of Galata (καστελλίου τών Γαλάτων), located near a small cape on the southeastern shore of Galata, was an important feature of Constantinople’s defenses, because it protected the northern side of the legendary chain protecting the Golden Horn. Now functioning as a mosque (Yeraltı Camii “Underground Mosque”), it is a multi-layered structure that provides a continuous link from the Byzantine and Ottoman periods to the present. During the Byzantine era, it was first a typical defensive structure and later a fortified arsenal under the Genoese, while it served many functions during the Ottoman era, including an arsenal, granary, customhouse, and mosque.

Throughout much of its history, it was positioned along the shores of Galata near the beginning of the Golden Horn, though it is now about 50 meters inland. The surviving substructure surviving as a mosque consists of a series of piers and groin vaults that first functioned as the undercroft of the fort (kastellion). It has a rectangular plan, roughly measuring 50 x 40 meters, with 42 visible piers (though it originally had as many as 63 piers). Its walls are around 2.25 meters thick, except for its northeastern side, which is less than 2 meters thick. Its current height of the vault arches is around 270-280 meters, but its original floor might lower than its current level.

The Fort of Galata was first mentioned during the Second Siege of Constantinople (717-718) when Leo III the Isaurian (717-741) blocked off the Golden Horn with a chain and equipped his navy with Greek fire. The fort served as a point of attachment for this chain that stretched across the mouth of the Golden Horn on enormous logs to the Tower of Kentenarion near the Acropolis in Constantinople. It is unclear when the fort itself was built, but it possibly dates to the reign of Tiberius III (698-705). At some point, at least by the 10th century it had at least one tower as well. Nikephoros II Phokas (963-969) made use of the chain during naval raids by the Rus’ in 969.

The Fort of Galata played a key role in the Fourth Crusade and the conquest of Constantinople in 1204. The Crusader naval assault, led by the Venetians, attacked the fort in July 1203 rather than the ships defending the Golden Horn behind the chain. Once the chain was broken, the Venetians quickly overcame what remained of Byzantine naval forces in the Golden Horn – forever ending of glory of the Byzantine navy and its dromons. Controlling the Golden Horn also made it easier for the Crusaders to sack Constantinople in April 1204. Michael VIII Palaiologos (1259-1282) failed in his attempt to take the fort in 1260 from the Latins, though he would take control of the fort the following year when he reconquered Constantinople.

In 1261, the Empire of Nicaea and the Republic of Genoa made an alliance at Nymphaeum to retake Constantinople from the Latin Empire. Despite strained relations in the aftermath of the reconquest of Constantinople, the Genoese were granted land in Galata in 1267. Before Galata came into the possession of the Genoese, its fortifications were demolished, except for the Fort of Galata, which would remain in Byzantine hands. It is unclear exactly when the Genoese began to build the walls of Galata, though evidence becomes clearer after 1315. By the time it became a possession of the Genoese, it was known as the Castle of Holy Cross (Castrum Sancte Crucis). It is uncertain when it actually it was handed over, though it was certainly by the year 1384. Around this time the Tower of the Holy Cross was added to the structure, over which a gilded cross was placed in 1391. A bell was also added to the fort in 1390, which perhaps was used to give warning signals. Eventually the fort was linked to the walls of Galata, during which time it also began to function as an arsenal and storehouse. It continued to have this function after the Genoese surrendered Galata following the Ottoman conquest of Constantinople in 1453.  

While the chain was used as not part of the Ottoman defenses, the building - known as Mahzen-i Sultani (“Imperial Magazine”) - retained its use as an arsenal magazine for the storage of gunpowder, as it was close to cannon foundries of Tophane established by Sultan Mehmet II. The structure was damaged by an explosion caused by lightening in the early 1500s. By the mid 16th century, a lead hipped roof was added to the restored structure known as Kurşunlu Mahzen (“Leaded Magazine”) and it was used as a granary. In 1676, the granary became the Galata Customhouse, when it functioned as the main storehouse of the Galata maritime customs. Only its walls remained after its roof burned down in 1683. In 1716, an imperial pavilion (Kurşunlu Mahzen Köşkü) was built on its southwest corner for Sultan Ahmed III. In the reign of Mahmud I (1730-1754), a sufi Naqshbandi (sufi) sheik from Damascus had a dream that led to the discovery of leaded coffins of three companions of the Prophet (Vehb bin Huseyre, Amr bin As, and Süfyan bin Uyeyne) who took part in the Umayyad sieges of Constantinople. The substructure was then converted into a mosque in 1752, during which time its round tower was used as a minaret until its collapse in 1766. After being damaged by a fire in 1819, the pavilion was restored in 1822 and was used as an office for the port authority until it was destroyed by a fire in 1870. A series of public health (quarantine) offices related to the port authority were built in the late 19th century, before the mosque was restored in 1908-1910.

Second Umayyad Siege of Constantinople in 716-717 from the Chronicle of Theophanes Confessor:

Now Masalmas, after he had wintered in Asia, was awaiting Leo's promises. But when he had received nothing from Leo and realized that he had been tricked, he moved to Abydos, crossed over to Thrace with a considerable army, and advanced towards the Imperial City.llb He also wrote to the Caliph Souleiman that the latter should come with the fleet that had been fitted out in advance. After devastating the Thracian forts, Masalmas laid siege to the City on 15 August. [The Arabs] fenced the land walls all round by digging a wide trench and building above it a breast-high parapet of dry stone. On 1 September of the first indiction Christ's enemy Souleiman sailed up with his fleet and his emirs. He had enormous ships, military transports, and dromones to the number of 1,800. He put in between the Magnaura and the Kyklobion. Two days later a south wind blew, and they set out from there and sailed past the City. Some of them crossed over to [the suburbs] of Eutropios and Anthemios, while others put in on the Thracian side, from the fort of Galata all the way to the Kleidion. Since the big ships were heavily laden and moved slowly, some twenty transports protected the rear, each one of them guarded by a hundred men clad in corselets. These found themselves becalmed in the midst of the current and, when a slight breeze blew down the straits, they were pushed back. Straight away, the pious emperor sent against them the fire-bearing ships from the Acropolis and, with divine help, set them on fire, so that some of them were cast up burning by the sea walls, others sank to the bottom with their crews, and others were swept down flaming as far as the islands Oxeia and Plateia. As a result, the inhabitants of the City took courage, whereas the enemy cowered with fear after experiencing the efficacious action of the liquid fire: for they had intended to beach their ships that evening by the sea walls and set their steering paddles upon the battlements. But God brought their counsel to nought through the intercession of the all-pure Theotokos. That same night the pious emperor stealthily drew up the chain on the Galata side. The enemy, however, thinking that the emperor had drawn it aside with a view to entrapping them, did not dare move in and anchor on the inside of Galata. Instead, they sailed up to the bay of Sosthenion and made their fleet secure there.

Chain of the Golden Horn at Istanbul Arc

Section of the Golden Horn chain 

Istanbul Archaeological Museums

Raid by the Rus’ in 969 from the History of Leo the Deacon

Meanwhile, when the Roman emperor Nikephoros learned about the situation with the Taurians [Rus’], since he was always careful and vigilant throughout his entire life, and was never drowsy, nor did he become enslaved by certain pleasures (for no one could say that he had seen him indulging in revelry even during his youth), he then seemed to be everywhere at once. He began to equip the infantry, to arm the companies, to draw up the cavalry regiment in depth, and to display the ironclad horsemen. In addition, he had artillery engines made and set them up on the walls of the city. He also secured to the tower that is usually called Kentenarion a very heavy chain made of iron, attached it to enormous logs, stretched it next to the Bosporos, and fastened it to a tower of the Kastellion on the other side. Since he was more effective and wiser than anyone we know of, he did not think it expedient to war against both peoples. Therefore he decided it would be a good idea to win over one of the peoples, for thus he thought he could prevail over the other very easily and subdue it in a shorter time.

Chain of the Golden Horn at Istanbul Mil

Section of the Golden Horn chain 

Istanbul Archaeological Museums

Crusaders attack the Fort of Galata in July 1203 from the Annals of Niketas Choniates

Not many days had elapsed before the Latins, realizing that there was no one to oppose them on land, came ashore. The cavalry moved out a short distance from the sea, and the long ships, dromons, and round warships moved inside the bay. Both the land and sea forces mounted a joint attack against the fortress, to which the Romans customarily fastened the heavy iron chain whenever an attack by enemy ships threatened, and forthwith they assailed the fortification. It was a sight to behold the defenders fleeing after a brief resistance. Some were slain or taken alive, and others slid down the chain as though it were a rope and boarded the Roman triremes, while many others lost their grip and fell headlong into the deep. Afterwards, the chain was broken, and the entire fleet streamed through. As for our triremes, some were overpowered on the spot, and those forced to shore suffered damage after they were emptied of their men. The evil took many forms, such as has never entered the heart of man.

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


Plan by Eldem


Hypothetical reconstruction by Özçakır

Map of Galata by Wolfgang Müller-Wiener

Blue indicates location of tower and chain



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

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

Köşkler ve Kasırlar Vol. 2 by SH Eldem

“Kastellion” İstanbul Ansiklopedisi by A. Berger

“Yeraltı Cami” İstanbul Ansiklopedisi by S. Eyice

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

Crusaders attack the Fort of Galata in July 1203 from the Annals of Niketas Choniates

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


The Chronicle of Theophanes Confessor translated by Mango, Scott, and Greatrex

The History of Leo the Deacon: Byzantine Military Expansion in the Tenth Century translated Talbot and Sullivan

O City of Byzantium: Annals of Niketas Choniates translated Harry J. Magoulias


Galata Album (Byzantine Legacy Flickr)

Golden Horn Chain Album (Byzantine Legacy Flickr)

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