The looser tribal organization of the Aetolians of NW Greece gave way during the 4th cent. bce to a *federal state, or league, which soon acquired considerable power. This increased dramatically in the first part of the 3rd cent. bce, owing to the Aetolians' role in the victory over the invading Gauls (280/79) and their control of the Delphic *amphictiony which soon followed (from 277). Normally hostile to Macedon, they became allies of Rome against *Philip (3) V of Macedon in 212 or 211 bce, Rome's first allies in mainland Greece. After a period of estrangement they allied themselves with Rome against Philip once again (199 bce), but such was their feeling of ill-treatment at the hands of the Romans in the aftermath of Philip's defeat at *Cynoscephalae (197 bce) that they went on to make common cause with the Seleucid king *Antiochus (3) III.