Aetolian League, confederation centering in the cities of Aetolia. It was formed in the 4th cent. BC and began to gain power in the 3d cent. in opposing the Achaean League and the Macedonians. At its height, the league stretched across Greece from sea to sea, including Locris, Malis, Dolopes, part of Thessaly, Phocis, and Acarnania. Its federal structure consisted of a popular assembly of all citizens, a federal council in which representation was based on the size of a community's military contingent in the Legion's army, and an inner council. The league could levy taxes, raise armies, and conduct foreign policy. The members also shared a common currency and a uniform system of weights and measures. In alliance with the Romans, the Aetolians helped to defeat Philip V of Macedon at Cynoscephalae in 197 BC However, the Aetolians became increasingly dissatisfied with Roman interference in Greek affairs and subsequently allied themselves with Antiochus III of Syria. His defeat (189 BC) by the Romans spelled the ruin of the league. Although formally it continued, its power had vanished.