In 221 BC, the Aetolians began pillaging the territory of Messenia. In 220 BC, the council of the Achaean League met in Aegium to discuss the city of Messene's request for their help. Most council members did not want to attack the Aetolians, but Aratus was able to persuade them. He began to raise an army near Megalopolis, with the aim of trapping the Aetolians as they returned to their ships to sail home. But the Aetolian commander was able to evade the threat. It seemed there would be no decisive confrontation, until the Achaean commanders made a crucial mistake and Aratus sent a cavalry unit against the Aetolians: