Located in Sariyer, Rumeli Fortress (Rumeli Hisarı) was constructed directly across from the Anadolu Hisarı (the Anatolian Fortress). Construction began in 1453 at the order of Sultan Mehmet the Conqueror placing the fortress at the narrowest point of the Bosphorous. The construction was completed in the short span of three months. Before the conquest of Istanbul it was used to protect against naval attacks. After the conquest it was used to as an inspection point for maritime traffic on the Bosphorous.
Over the centuries, the area inside the fortress filled with small wooden houses but in the course of restoration work in 1953 these houses were removed. After its restoration, the fortress came to be known for the numerous concerts given here during the summer months, and it now serves as an open air theater and museum.