 The Allies initially adopted a strategy of blocking land and sea approaches to southern Greece.Thus, in August 480 BC, after hearing of Xerxes' approach, a small Allied army led by Spartan King Leonidas I blocked the Pass of Thermopylae, while an Athenian-dominated navy sailed to the Straits of Artemisium.Famously, the massively outnumbered Greek army held Thermopylae for three days before being outflanked by the Persians, who used a little-known mountain path.