This is the Rumeli Hisar, a fortress built in 1452 on the orders of Fatih Mehmet. It was originally called Boğaz-kesen, which according to Strolling through Istanbul (Redhouse) was a "sort of pun which means both cut-throat and "cutter of the straight". Its purpose was - together with the Anadolu Hisar on the other side - to cut the city off from communication with and possible aid from te Black Sea. It was built in four months. For a photographic visit to the fortress, it has a special gallery: Rumeli Hisarı.