Expansion of Macedonia under Philip II a significant problem, blocking the main route into Greece. However, a second route into central Greece was available. In 480 BC, during the Battle of Thermopylae, the Persian king Xerxes had sent his army via a mountain track (the "Anopea") to outflank the pass. From this track, on the western side of Mount Kallidromon, another road led off and descended in Phocis. In 480 BC, a thousand Phocian troops were stationed above Thermopylae to guard the road and prevent a Persian assault on Phocis (though they notably failed to prevent the Persians using "Anopea"). However, in 339 BC, the Greeks
Gauls army, defeated Bolgius and repelled the invading Gauls. In the second Gaulish invasion of Greece (278 BC), the Gauls, led by Brennos, suffered heavy losses while facing the Greek coalition army at Thermopylae, but helped by the Heracleans they followed the mountain path around Thermopylae to encircle the Greek army in the same way that the Persian army had done at the Battle of Thermopylae in 480 BC, but this time deafeating the whole of the Greek army. After passing Thermopylae the Gauls headed for the rich treasury at Delphi, where they were defeated by the re-assembled Greek army. This