Dardanelles

The Dardanelles separates the Gallipoli peninsula from the Asian shore, joining the Aegean to the Sea of Marmara and the route onward to the Black Sea. Its surface current runs toward the Aegean, while denser salt water flows in the opposite direction below. During the Ottoman–Venetian wars, the strait became a contested approach to Istanbul. In 1659 the Ottomans built Seddülbahir and Kumkale on opposite shores to defend its entrance against Venetian attack.