Sea Of Anc. Propontis (Marmora), a body of water lying between European and Asiatic Turkey; length 172 m., greatest breadth about 50 m. Its N. E. extremity is connected with the Black sea by the Bosporus, and its S. W. extremity with the Archipelago by the Dardanelles. It is remarkable for its depth, which in some places is more than 350 fathoms. It has numerous excellent harbors on its N. shore, contains several islands, the principal of which is Marmora, and receives the waters of many but inconsiderable tributary streams. It has no tides, but currents of variable strength and velocity run through it. (See Black Sea, vol. ii., p. 683.) Its shores present a picturesque aspect, and are especially bold and precipitous on the Asiatic side. - The Island of Marmora (anc. Proconnesus; Turk. Marmar Adassy), which gives name to the sea, is about 12 m. long and 6 m. wide, and for the most part mountainous and barren. It has been celebrated from a remote age for its marble (whence its name, from Lat. marmor), with which in ancient times it supplied Oyzicus and other Hellenic cities, as in modern times it has supplied Constantinople. The capital, Marmora, stands on the S. W. coast, and is chiefly built of wood.

The highest summit of the island is in lat. 40° 30' N., Ion. 27° 35' E.