Mehmed refused the offer of peace proffered, and proceeded with his siege plans by commissioning the construction of a large fortress that would be used to control all sea traffic along the Bosphorus, and would work together with the older Anadoluhisari (Anatolia Fortress) on the strait to prevent any possible maritime aid from reaching Constantinople during the final Ottoman siege of the city in 1453, particularly from Genoese colonies along the Black Sea, such as Caffa, Sinop and Amasra.