Epirus was an ancient region of Greece, located in what is now Albania and northwestern Greece, with Illyria to the north, the Pindus mountains to the east, and the Gulf of Ambracia (near Preveza) to the south. The region was barbarous in early Greek times and famous primarily for the oracle at Dodona (in southern Epirus) with its sacred oak tree and cult of Zeus.
The oracle was much consulted throughout ancient times. The region became Hellenized through contact with Corcyra (Korfu) and Ambracia
, but it did not become important until Alexander, king of Molossia (in Epirus) and brother-in-law of Philip II of Macedonia, unified the Epirotes. Alexander invaded Italy in 333 B.C. He conquered much of southern Italy, but was finally defeated and killed in 330. When Pyrrhus (319–272) ascended the throne, Epirus was dependent on Macedonia. He made his country independent and increased its territory at Macedonia's expense. He too invaded Italy brilliantly but unsuccessfully. His failure weakened the kingdom, which fell c.232. Epirus was subsequently drawn into the Roman-Macedonian wars, and in 167 the Romans sacked the country and enslaved 150,000 Epirotes. For centuries thereafter, Epirus remained under Roman (and later Byzantine) rule. In 1081 it was conquered by the Norman crusader Robert Guiscard. When the Fourth Crusade captured Constantinople, the Byzantines established (1204) an independent despotate of Epirus. It survived as a vassal state of the Byzantine Empire until conquered by the Ottoman Turks in the 15th century.
Charles W. Fornara, Academic American encyclopedia, Volume 7, Grolier, 1997: