The Bosphorus is a strait that forms part of the boundary between Europe and Asia. Along with the Dardanelles, it is one of two straits in Turkey. The world's narrowest strait used for international navigation, it connects the Black Sea with the Sea of Marmara (which is connected by the Dardanelles to the Aegean Sea, and thereby to the Mediterranean Sea.)
The Bosphorus' limits are defined as the connecting line between the lighthouses Rumeli Feneri and Anadolu Feneri in the north and between the Ahırkapı Feneri and the Kadıköy İnciburnu Feneri in the south.
The strait is between the limits 31 km (17 nmi) long, with a width of 3,329 m (1.798 nmi) at the northern entrance and 2,826 m (1.526 nmi) at the southern entrance. Its maximum width is 3,420 m (1.85 nmi) between Umuryeri and Büyükdere Limanı, and minimum width 700 m (0.38 nmi) between Kandilli Point and Aşiyan.