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
Battle of Thermopylae he selected only Spartans with living sons. The Spartan force was reinforced "en route" to Thermopylae by contingents from various cities and numbered more than 7,000 by the time it arrived at the pass. Leonidas chose to camp at, and defend, the "middle gate", the narrowest part of the pass of Thermopylae, where the Phocians had built a defensive wall some time before. News also reached Leonidas, from the nearby city of Trachis, that there was a mountain track that could be used to outflank the pass of Thermopylae. Leonidas stationed 1,000 Phocians on the heights to prevent such a