After the naval victory at Cyzicus, the ancient Athenian general Alcibiades possibly built a custom station for ships coming from the Black Sea on a small rock in front of Chrysopolis (today's Üsküdar). In 1110 Byzantine Emperor Alexius Comnenus built a wooden tower protected by a stone wall. From the tower an iron chain stretched across to another tower erected on the European shore, at the quarter of Mangana in Constantinople. The islet was then connected to the Asiatic shore through a defense wall, whose underwater remains are still visible. During the Ottoman conquest of Constantinople (Istanbul) in 1453, the tower held a Byzantine garrison commanded by the Venetian Gabriele Trevisano. Subsequently, the structure was used as a watchtower by the Ottoman Turks during the reign of Sultan Mehmed the Conqueror.