An ancient country lying west of Istanbul and the Black Sea and north of the Aegean, now part of modern Turkey, Greece, and Bulgaria. It extended as far west as the Adriatic but the Thracians retreated eastwards between the 13th and 5th centuries bc under pressure from the Illyrians and Macedonians. Conquered by Philip II of Macedon in 342 bc it later became a province of Rome. The region was ruled by the Ottoman Turks from the 15th century until the end of World War I, but northern Thrace was annexed by Bulgaria in 1885. In 1923 all of Thrace east of the Maritsa River was restored to Turkey.