The city had been attacked many times before the final siege by the conqueror in 1453, but the Roman city was enabled the city to resist. Even during long sieges, provisions were brought into the city from sea. To prevent any reinforcements and help coming from the Black Sea during the final siege, Mehmet the Conqueror built a fortress on the European shore, opposite the earlier Turkish fortress on the Asian shore.
The fortress was completed in the amazingly short time of four months in 1452. This largest and strongest fortress of the Middle Ages was no longer important after the fall of the city. This fine example of classic Turkish fortress architecture is another adornment of the Bosphorus. It was restored in the 1950s and turned into a museum. During the annual Festival of Arts, the fortress gardens are used as an amphitheatre.
The best view of the fortress is from the Asian side of from the boats operating on the Bosphorus. The campus of the Bosporus University is on the slopes behind the fortress. This was formerly Robert Collage, the first American educational instution established outside the United States; in 1971, the collage became Bosphorus (Boğaziçi) Universty.
The Anatolia Fortress is located where the Göksu Stream meets the Bosphorus. It was constructed in 1395 by Sultan Yıldırım Beyazid. Sultan Mehmed II added external walls when he was having the Rumeli Fortress built. After the conquest of Istanbul , the Anatolia Fortress built lost its military importance. The area around it slowly began to turn into a residential area. The fortress consists of the inner and outher areas and the walls surrounding them. When the fortress was first constructed, there was no entrance gate, nut the fortress was entered via suspension bridge that went over the inner walls. A wooden staircase led to the upper sloors of the tower. The walls of the main castle measure 65 meters from east to west and 80 meters from north the south, measuring 2.5 meters in width. There are strategically placed hotels for cannons on the outher walls. Today, some part of the fortress have been demolished and a road passes trough the middle.