In ancient times Epirus ("mainland" as opposed to the offshore islands) was the mountainous coastal district bordered by Illyria, Macedonia and Thessaly. To the south lay Aetolia. Epirus was separated from Illyria to the north by the Ceraunian Mountains, and by the famous Pindus River flowing from Thessaly. The Acheron river, mythologized as a river of Hades, flowed through this region, and here also stood the oak grove of Dodona (modern Dodoni), sacred to Zeus and famous for its oracles.
Ancient Epirus was a homeland of the Dorian people, whose invasion of Greece in the tenth century BC initiated the Dark Ages of Greece. Though the mother of Alexander the Great was an Epirote princess, wild and tribal Epirus, famous for cattle and horses, lay outside the mainstream of Greek culture, though Greek trading colonies such as Corinth's Ambracia were established along its coast, until it was vigorously Hellenized by its most famous ruler, Pyrrhus, (318 BC - 272 BC). Pyrrhus, King of Epirus, one of the monarchs who divided the empire of Alexander the Great, was known for his campaigns against the Romans in Italy (see also Pyrrhic victory) and for his brief rule of Macedonia.
With the fall of the Byzantine Empire in 1204 to Venetian-led armies in the Fourth Crusade, the Despotate of Epirus became one of the three successor states, the others being the Empire of Nicaea, and Trebizond. At its brief height the despotate controlled territory from Durazzo in the north to the Gulf of Patras in the south, even the island of Corcyra (Corfu). The Despot was defeated by armies of the Nicaean lineage, who later re-captured Constantinople from the Latins in 1261 and re-formed the Byzantine Empire.