The Harbor of Theodosius, also simply called the Arsenal, was the largest of the ports found in Constantinople, the capital of the Byzantine and Ottoman Empires. The harbor was located on the south side of the peninsula where the city was built, facing towards the Sea of Marmara.
The port, originally called the Harbor of Eleutherios, was augmented by Emperor Theodosius I in the 4th century, earning its current name. It would go on to become a major venue for trade of agricultural goods, as well as a military outpost.
In 1511, the Assassin Ezio Auditore da Firenze incited a riot within the harbor, by using heralds to speak to nearby civilians about the abuse of power by the Janissaries. The rioters banded together in forcing open the Arsenal gates, setting fires and attacking the Janissaries, while Ezio used the confusion within as an opportunity to seek out a member of the Templar Order, Manuel Palaiologos.
Ezio tailed Manuel and his fellow Templar Shahkulu to a small warehouse, where a shipment of firearms had been delivered. After observing a brief meeting between Shahkulu, Manuel and Tarik Barleti, Ezio fled the harbor in an attempt to alert his fellow Assassins. Upon arriving back at the Arsenal gates, Ezio found nearly all of the rioters slaughtered, and left the harbor.
The following year, in 1512, after discovering the murder of the Assassin leader Yusuf Tazim, as well as the kidnap of Sofia Sartor, Ezio led the Ottoman Assassins in a large scale attack on the harbor, in which Prince Ahmet and his Byzantine forces were stationed.
There, the Assassins engaged with a large number of soldiers, and eventually cornered their commander. However, Ezio was forced to allow the Templar to escape, as Sofia was still being held hostage.
During later Ottoman rule in the 1500s, a large amount of silting – or the building up of sediments along the bank – forced the port to be closed, and eventually built over. Similar activity continued until, in the 17th century, the harbor had all but disappeared.
In the 21st century, the site was excavated, and workers discovered the remains of dozens of ancient Byzantine galleys deep within the soil.