Marmara, Sea of, or Sea of Marmora, c.4,430 sq mi (11,474 sq km), NW Turkey, between Europe in the north and Asia in the south. The Sea of Marmara, c.175 mi (280 km) long and 50 mi (80 km) wide, is connected on the east with the Black Sea through the Bosporus and on the west with the Aegean Sea (part of the Mediterranean Sea) through the Dardanelles. İstanbul (Constantinople) is located at the entrance of the Bosporus into the Sea of Marmara. The sea has no strong currents and the tidal range is minimal. In ancient times the sea was known as Propontis [Gr., = fore-sea] from its position relative to the Black Sea. Its modern name is derived from the small island of Marmara or Marmora (ancient Proconnesus ), famous for its extensive marble quarries.