The Despotate of Epirus was the Greek successor state in north-western Greece that briefly held Thessalonica and claimed the empire, and lost both to Bulgaria in a single afternoon in 1230.
Epirus is the mountainous north-western corner of Greece, and it produced the successor state that came closest to reaching Constantinople first.
Founded by Michael I Komnenos Doukas after 1204, it expanded east under his half-brother Theodore, took Thessalonica from the Latins in 1224, and had Theodore crowned emperor there — a direct challenge to Nicaea's claim.
In 1230 Theodore attacked Bulgaria and was destroyed at Klokotnitsa. Epirus never recovered its position, and thirty years later it withdrew from the field at Pelagonia and left the anti-Nicaean coalition to be destroyed without it.
Michael I Komnenos Doukas was a cousin of the last pre-1204 emperors, and he established himself in Epirus in the confusion after the Fourth Crusade with the support of local landowners.
The terrain did most of the work. Epirus is defensible, poor and hard to reach, and the Latin Empire never had the resources to take it seriously.
His half-brother Theodore, who succeeded in 1215, was the aggressive one: he captured the Latin emperor-elect Peter of Courtenay in 1217, took Thessalonica in 1224, and by 1225 was campaigning in Thrace within reach of Constantinople itself.
Michael I Komnenos Doukas (1205–1215) founded the state and secured the mountains.
Theodore Komnenos Doukas (1215–1230) took Thessalonica, was crowned emperor there by the archbishop of Ohrid, and lost everything at Klokotnitsa — captured, later blinded, and reduced to a political nuisance for the rest of his life.
Michael II Komnenos Doukas (1230–1268) rebuilt the state as a regional power, married his daughters into Achaea and Sicily to build the coalition of 1259, and then withdrew his troops from the field at Pelagonia — the decision that ended any Epirote claim to the empire.
In 1230 Theodore invaded Bulgaria in breach of a treaty, and Ivan Asen II met him at Klokotnitsa on the Maritsa. The Epirote army was destroyed and Theodore was captured.
The story that circulated afterwards — that Asen carried the broken treaty on a lance as a banner — may be embellishment, and the result is not: the empire of Thessalonica collapsed within a few years and Epirus was pushed back to where it had started.
Nicaea took Thessalonica in 1246, and after that there was only one Greek claimant to Constantinople that anybody took seriously.
Epirus survived as a principality at Arta for two more centuries, passing through Greek, Italian and Albanian rulers before the Ottomans took it in 1449.
Its churches are its most visible legacy: the Paregoretissa at Arta and the other late Byzantine foundations of the despotate are among the best-preserved buildings of the period anywhere in Greece.
Its historical importance is as the road not taken. For six years in the 1220s it was more likely than Nicaea to restore the empire, and the difference was one battle it chose to fight against the wrong enemy.