In 243 BC, exhorted by Aratus of Sicyon, Megara expelled its Macedonian garrison and joined the Achaean League, but when the Achaeans lost control of the Isthmus in 223 BC the Megarians left them and joined the Boeotian League. Not more than thirty years later, however, the Megarians grew tired of the Boeotian decline and returned their allegiance to Achaea. The Achaean strategos Philopoemen fought off the Boeotian intervention force and secured Megara's return, either in 203 or in 193 BC.