Anadoluhisarı, constructed on an area of 7,000 m², is situated at the narrowest point with 660 m of the Bosporus strait and next to a creek named Göksu (ancient Greek name: Aretòs). The Fatih Sultan Mehmet Bridge, the second bridge spanning Bosporus, is located just north of the fortress. Another fortress, Rumelihisarı, was built between 1451 and 1452 by Sultan Mehmed II opposite of Anadoluhisarı on the European side in order to obtain absolute control over the sea traffic of the Bosporus Strait, which was especially vital for the Genoese in Galata, who were allied with the Byzantines and had colonies in the Black Sea such as Caffa, Sinop and Amasra.