Montreux Convention, June, 1936, an international agreement signed at Montreux, Switzerland. Turkey was given the right to fortify the Dardanelles and Bosporus straits, which link the Black and Mediterranean seas. (The Treaty of Lausanne, 1923, had forbidden the Turks to do so.) After World War II the Soviet Union insisted on a share in the defense of the straits, but dropped its demands in 1953.