Big Diomede Island (Russian: остров Ратманова, ostrov Ratmanova, native name Imaqliq) is an island among the Diomede Islands in the middle of the Bering Strait. The island is a part of the Chukotsky District of the Chukotka Autonomous Okrug of Russia.
Big Diomede Island is located about 45 km (28 mi) southeast of Cape Dezhnev on the Chukchi Peninsula and is Russia's easternmost point. The International Date Line is about 1.3 km (0.81 mi) east of the island.
The island was originally inhabited by Yupik Eskimos. During the Cold War all local population was forcibly moved to Chukotka in order to prevent contacts with American Little Diomede island Inupiat inhabitants. Unable to assimilate or live among Russians, they have perished.
The first European to reach the islands was the Russian explorer Semyon Dezhnev in 1648. The Danish navigator (in Russian service) Vitus Bering re-discovered the Diomede Islands on August 16, 1728, the day on which the Russian Orthodox Church celebrates the memory of the martyr St. Diomede.
In 1732, the Russian geodesist Mikhail Gvozdev plotted the island's map.
In 1867 during the Alaska Purchase the new border between the nations was drawn right between the Big Diomede and Little Diomede islands.
During the Cold War, that line between Big Diomede and Little Diomede constituted the border between the USA and the Soviet Union, and became known as the "Ice Curtain". In 1987, Lynne Cox swam from Little Diomede to Big Diomede and was congratulated jointly by Mikhail Gorbachev and Ronald Reagan.