Andoluhisari Fortress is situated at the narrowmost point of the Bosporus, The complex is the oldest surviving Turkish architectural structure built in Istanbul built 1393-4. Mehmed II further built a sister structure to Anadoluhisarı across the Bosphorus called Rumelihisari (fortress)The two fortresses worked in tandem in 1453 to throttle all maritime traffic along the Bosphorus, thus helping the Ottomans achieve their goal of making the city of Constantinople (later renamed Istanbul) their new imperial capital.