Rumelihisarı (also known as Rumelian Castle and Roumeli Hissar Castle) is a fortress located in the Sarıyer district of Istanbul, Turkey, on a hill at the European side of the Bosphorus. It gives the name of the quarter around it. It was built by the Ottoman Sultan Mehmed II between 1451 and 1452, before he conquered Constantinople. The three great towers were named after three of Mehmed II's viziers, Sadrazam Çandarlı Halil Pasha, who built the big tower next to the gate, Zağanos Pasha, who built the south tower, and Sarıca Pasha, who built the north tower.