BOSPORUS or BOSPHORUS. By the ancients this name, signifying a strait, was especially applied to the Bosporus Cisn merius (see below), and the Bosporus Thracius (Gr. Booiropos ox-f ord, traditionally connected with Io, who, in the form of a heifer, crossed the Thracian Bosporus in her wanderings). It now denotes the latter strait, which unites the Black sea with the Sea of Marmora and forms part of the boundary between Europe and Asia. The channel is 18m. long, and has a maximum breadth at the northern entrance of 24m., a minimum breadth of about 800yd., and a depth varying from 20 to 66 fathoms in mid stream. In the centre there is a rapid current from the Black sea to the Sea of Marmora, but in the opposite direction a counter current sets in below the surface and along the shores. The scen ery on both sides is varied and beautiful, determined by a great variety of volcanic rocks in the north, and of sandstones, conglom erates and calcareous deposits elsewhere. Many villages line each well-wooded shore, while on the European side are numerous fine residences of the wealthy class of Constantinople. By treaty of 1841, confirmed by the Treaty of Berlin in 1878 and at other times, no ship of war other than Turkish may pass through the strait (or through the Dardanelles) without the countenance of the Turkish authorities. They in turn are under the control of an International Straits commission which is in permanent ses sion at Constantinople, and was established in 1918. (See also CONSTANTINOPLE.)