Galata Tower, one of the major landmarks of modern Istanbul, was built in the mid-14th century when the Genoese had a colony at Galata. This tower, which has long dominated the topography of the region, functioned as the donjon (keep) of the Genoese fortification system of Galata. The first construction phase of the Walls of Galata began in the early 14th century and continued to be expanded and strengthened until shortly before the Ottoman conquest of Constantinople in 1453. The Kastellion (Galata’s older fortress probably dating to the 8th century) was incorporated into the Genoese fortifications by the late 14th century. The local municipality began to demolish much of the walls in 1864, though several sections of the walls, multiple towers, and a gate still survive.

Sykai, as Galata was known in antiquity, probably received its first fortifications in the 5th century, though they were traditionally attributed to Constantine I. Justinian I restored Sykai and its walls in the 6th century, after which it was called Justinianopolis. The surviving fortifications of Galata were demolished by the Byzantines just before they granted the Galata region to the Genoese in 1267, following their recovery of Constantinople in 1261. The only exception was the Kastellion, which would remain in Byzantine hands for the next century. The earliest borders of the Genoese quarters of Galata (officially known as Pera) are uncertain, but the limits of the quarter were clearly delineated in 1303 – officially granting a relatively long, narrow strip of land along the southern shore of Galata west of the Kastellion.

A series of attacks followed this land grant, which eventually resulted in the Genoese building fortifications to protect their quarter. In the first year of the Byzantine-Venetian War of 1296-1302, a Venetian fleet set fire to the buildings of the defenseless Genoese quarter at Galata, while its inhabitants sought refuge behind the walls of Constantinople. Following their arrival in Constantinople in 1303, the Catalan Company was involved in a conflict with the Genoese, allegedly resulting in 3000 Genoese deaths. While Andronikos II managed to stop the Catalans from pillaging Galata, this threat further emphasized the Genoese’s need for security. An agreement was made between the Byzantines and Genoese in 1304, which extended their colony, giving permission for the existing moats and allowing for the construction of fortified civic buildings that would provide security in their quarters. It strictly prohibited fortified walls, but allowed for other buildings, including a slaughterhouse, marketplace, loggia, baths, church, and weigh house.

It is unclear exactly when the Genoese began to build the walls of Galata. In 1306 and again in 1308, the Genoese were purchasing land beyond the borders granted by the emperor and at the same time building a series of fortified civic buildings within the official quarters that were converted into defensive “tower houses” with windows modified into arrow slits.

Much of the quarter including the Palazzo Comunale (the municipal palace of the podestà, Galata’s chief magistrate) burned down in 1315 and was rebuilt in 1316. Sometime between 1304 and 1316, it seems that proper fortified walls were also built between the tower houses, despite the prohibitions in the previous agreement. During a secondary phase of construction, a small rectangular castle was built on the western flank of the Palazzo Comunale by 1335, when other fortifications were being built on the hill north of the granted quarter. During this phase of construction, the height of the walls was increased. Following their occupation of Mytilene in 1333, the Genoese began to illegally expand their quarter at Galata. In 1336, when Andronikos III recaptured Lesbos from the Genoese, the emperor ordered the walls towards the hill to be demolished, though it is unclear how well this was implemented. This secondary construction phase of the fortifications also corresponds to a series of wars, starting with the civil war (1341-1347) between John V Palaiologos and John VI Kantakouzenos. While they had been given permission by Kantakouzenos to purchase adjacent vineyards, the Genoese expanded and fortified their quarters far beyond this area, building Galata Tower on the hilltop around the end of 1348. The Genoese withdrew from the hill when the Byzantine-Genoese war of 1348-1349 came to an end. Kantakouzenos then returned it in 1349, as a clear signal that the Genoese must have imperial consent and could not act against the interests of the empire. This war, which began over a dispute over customs duties, also saw the destruction of the imperial fleet and a major fire in Galata.

In 1351, the Byzantines unsuccessfully attempted to capture Galata. The next major construction phase of Galata’s walls took place after the Byzantines and Venetians were defeated by the Genoese in 1352, which concluded with a treaty officially extending the Genoese quarters of Galata to the east. It was extended until the "Castle of Holy Cross" (Castrum Sancte Crucis) in the east, which had previously been known as the Kastellion. Genoese archives indicate that the Tower of Holy Cross" (Turris Sancte Crucis) was attached to the Castle of Holy Cross in 1391, after a series of works that also included adding a gilded globus cruciger (cross with an orb) on top of the tower. 

Epigraphic evidence suggests the Genoese acquired the northwestern district in 1387, the western district Spiga in 1397, and the eastern district Lagirio around 1400, though archival documents suggest that the Genoese controlled Spiga by 1351 and Lagirio in 1376. Repairs made to the wall in 1390-1391 were likely made in expectation of an Ottoman attack, though the blockade of Bayezid I seemingly halted defensive constructions until 1435. An unsuccessful Ottoman siege of Galata took place in the late 14th century and again in 1411 and 1422. The Milanese occupation of Genoa in 1421-1435 likely slowed additional defensive construction. The last known pre-Ottoman slab records work in 1452 supported by Pope Nicholas V (1447-1455), who was of Genoese origin.  

Galata surrendered to the Ottomans in 1453 following the conquest of Constantinople. While Mehmet II promised that the fortifications of Galata would be spared, several primary sources mention that he ordered the walls to be demolished. However it is unclear to what extent the Ottomans actually demolished the walls, and except for reconstruction following the earthquakes of 1509 and 1635, these walls were largely extant until the late 19th century. Perhaps sources of the time mentioning the destruction of the walls only refer to the destruction of the upper sections of the walls which would have limited their defensive function. The earthquake of 1509 caused the upper levels of Galata Tower to collapse. Galata would continue to suffer from a sequence of fires and earthquakes over the next few centuries. The local municipality began to demolish the walls in 1864, though the walls were well documented before this began. The total number of the gates is unclear, but it had at least 6 maritime gates (some of which were linked to piers). A total of 25 gates of Galata Walls were recorded with their locations and names in the Ottoman period of Galata. Today only a few sections of the walls, some towers and a gate survive.

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Written with the help of Dr. Sercan Sağlam