Dardanelles, a strait in Turkey forming part of the waterway between the Aegean Sea (an arm of the Mediterranean Sea) and the Black Sea. On the north bank is the Gallipoli Peninsula of European Turkey, on the south is Asian Turkey. The Dardanelles follows a relatively narrow 40-mile (64-km) course between hills that rise abruptly from its banks. The strait is deep enough for the largest ships and varies in width from less than one mile (1.6 km) to more than 4 miles (6.4 km).

The Dardanelles is connected with the Black Sea through the Sea of Marmara and another strait, the Bosporus. For centuries, this waterway has been of great strategic and commercial value because it controls all sea traffic between the Black Sea and the Mediterranean Sea. The ancient Greeks called the strait Hellespont (“Helle's Sea,”in honor of a maiden who drowned in its waters). The name Dardanelles was taken from an ancient Greek city, Dardanus, on the Asiatic side of the strait.

The Dardanelles was crossed by Xerxes in 480 B.C. when he invaded Thrace. At the end of the Persian Wars (479 B.C.), Athens held control of the Dardanelles. During the Peloponnesian War (431-404 B.C.), Sparta gained control. In 334 B.C. the strait was crossed by Alexander the Great during his campaign against Asia Minor. When Constantinople was the center of the Byzantine Empire, the Dardanelles gained importance as a strategic passageway to the city. With the fall of the Byzantine Empire (1453), the Turks took control of the strait.

During World War I, in the Gallipoli Campaign, the Allies attempted to seize control of the strait but failed. An agreement at the Lausanne Conference (1922-23) made the Dardanelles an unfortified international waterway, but at the Montreux Conference (1936) the strait was returned to Turkish control. During most of World War II, it was closed to the Allies because Turkey remained neutral until late in the war.