In 340 BC, Philip started the siege of Perinthus, and in 339 BC, began another siege against the city of Byzantium. As both sieges failed, Philip's influence over Greece was compromised. He successfully reasserted his authority in the Aegean by defeating an alliance of Thebans and Athenians at the Battle of Chaeronea in 338 BC, and in the same year, destroyed Amfissa because the residents had illegally cultivated part of the Crisaian plain which belonged to Delphi. These decisive victories led to Philip being recognized as the military leader of the League of Corinth, a Greek confederation allied against the Persian Empire, in 338/7 BC. Members of the league agreed never to wage war against each other, unless it was to suppress revolution.