At the dawn of history the ancient Thracians—a group of tribes speaking an Indo-European language—extended as far west as the Adriatic Sea, but they were pushed eastward (c.1300 B.C.) by the Illyrians, and in the 5th cent. B.C. they lost their land west of the Struma (Strimón) River to Macedon. In the north, however, Thrace at that period still extended to the Danube. Unlike the Macedonians, the Thracians did not absorb Greek culture, and their tribes formed separate petty kingdoms.
The Thracian Bronze Age was similar to that of Mycenaean Greece, and the Thracians had developed high forms of music and poetry, but their savage warfare led the Greeks to consider them barbarians. Many Greek colonies—e.g., Byzantium on the Hellespont and Tomi (modern Constanţa) on the Black Sea—were founded in Thrace by c.600 B.C. The Greeks exploited Thracian gold and silver mines, and they recruited Thracians for their infantry. Thrace was reduced to vassalage by Persia from c.512 B.C. to 479 B.C., and Persian customs were introduced.
Thrace was united as a kingdom under the chieftain Sitalces, who aided Athens during the Peloponnesian War, but after his death (428 B.C.) the state again broke up. By 342 B.C. all Thrace was held by Philip II of Macedon, and after 323 B.C. most of the country was in the hands of Lysimachus. It fell apart once more after Lysimachus' death (281 B.C.), and it was conquered by the Romans late in the 1st cent. B.C. Emperor Claudius created (A.D. 46) the province of Thrace, comprising the territory south of the Balkans; the remainder was incorporated into Moesia. The chief centers of Roman Thrace were Sardica (modern Sofia), Philippopolis (Plovdiv), and Adrianople (Edirne).
The region benefited greatly from Roman rule, but from the barbarian invasions of the 3d cent. A.D. until modern times it was almost continuously a battleground. The northern section passed (7th cent.) to the Bulgarians; the southern section remained in the Byzantine Empire, but it was largely conquered (13th cent.) by the second Bulgarian empire after a brief period under the Latin Empire of Constantinople. In 1361 the Ottoman Turks took Adrianople, and in 1453, after the fall of Constantinople, all of Thrace fell to the Turks.
In 1878, N Thrace was made into the province of Eastern Rumelia; after the annexation (1885) of Eastern Rumelia by Bulgaria (which had gained independence in 1878), the political meaning of the term Thrace became restricted to its southernmost part, which was still in Turkish hands. The terms Eastern Thrace and Western Thrace were used for the territories east and west of the Maritsa River. In the first of the Balkan Wars (1912–13) Turkey ceded to Bulgaria all Western Thrace and the inland half of Eastern Thrace, including Adrianople, but after its defeat in the Second Balkan War (1913), Bulgaria retroceded all Thrace east of the Maritsa to Turkey.
After World War I, Bulgaria ceded the southern part of its share of Thrace to Greece by the Treaty of Neuilly (1919), thus losing its only outlet to the Aegean. By the Treaty of Sèvres (1920) Greece also obtained most of Eastern Thrace except the zone of the Straits and Constantinople; the treaty, however, was superseded by the Treaty of Lausanne (1923), which restored to Turkey all Thrace E of the Maritsa. As a result of subsequent population movements, the ethnic composition of the various parts of Thrace now corresponds largely to the national divisions. The Greek-Bulgarian frontier of 1919 and the Turkish-Greek frontier of 1923 were left unchanged after World War II, during which Bulgaria had occupied (1941–44) Greek Thrace.