in geography, denotes, in general, a narrow sea, or channel, separating two continents, and serving as a communication between two seas.

Bosporus is more particularly used for the straits of Constantinople, which divide Europe from Asia. This was the original Bosphorus, so called because oxen could swim over it; and from the resemblance between it and the straits of Kaffa, these last were anciently called the Gimmerian, and the former the Thracian Bosphorus. This strait, which is the communication between the Black sea, and that of Marmora, is about 20 miles in length, and a mile and a quarter in breadth where it is narrowest. The Turks have built two castles over against each other to defend the passage. The country about it is very pleasant: on one side stands Constantinople; and on the other Scutari, where the Grand Signior has a palace, and is looked upon as a suburb to Constantinople. The entrance of this strait is dangerous, and sometimes fatal to vessels.