Epirus (//) is a geographical and historical region in southeastern Europe, now shared between Greece and Albania. It lies between the Pindus Mountains and the Ionian Sea, stretching from the Bay of Vlorë and the Acroceraunian Mountains in the north to the Ambracian Gulf and the ruined Roman city of Nicopolis in the south. It is currently divided between the region of Epirus in northwestern Greece and the counties of Gjirokastër, Vlorë, and Berat in southern Albania. The largest city in Epirus is Ioannina, seat of the region of Epirus, with Gjirokastër the largest city in the Albanian part of Epirus.
A rugged and mountainous region, Epirus was the north-west area of ancient Greece. It was inhabited by the Greek tribes of the Chaonians, Molossians, and Thesprotians. It was home to the sanctuary of Dodona, the oldest oracle in ancient Greece, and the second most prestigious after Delphi. Unified into a single state in 370 BC by the Aeacidae dynasty, Epirus achieved fame during the reign of Pyrrhus of Epirus who fought the Roman Republic in a series of campaigns. Epirus subsequently became part of the Roman Republic along with the rest of Greece in 146 BC, which was followed by the Roman Empire and Eastern Roman Empire.
Following the fall of Constantinople to the Fourth Crusade, Epirus became the center of the Despotate of Epirus, one of the successor states to the Byzantine Empire. Conquered by the Ottoman Empire in the 15th century, Epirus became semi-independent during the rule of Ali Pasha in the early 19th century, but the Ottomans re-asserted their control in 1821. Following the Balkan Wars and World War I, southern Epirus became part of Greece, while northern Epirus became part of Albania.