This was built by Bayezit I (1389-1402), long before the conquest of Istanbul, at the end of the 14 century as the first step in bridging the gap to Byzantine lines,and to gain control of the Bosphorus.
It has been variously called “Yenice Hisar”, “Akca Hisar”, “Guzelce Hisar”. There is one main tower,with an inner tower and surrounding battlement walls.
In the 17 century a small mescit-chapel mosque-and open prayer place-namazgah were added. Mehmet the conqueror built the Rumelihisarı in 1452 and closed the Bosphorus traffic. Today,the fortress is an open air museum.