While the Persians were hesitating thus, a Greek shepherd, Ephialtes, stole into their camp, and, vile traitor that he was, offered to show them another way to get into Greece, if they would pay him well. This man was led into the tent of a Persian general, where he explained that he could easily lead a troop of Persians over the mountains.

By a goat path known to the Greeks only, it was possible not only to cross the mountains, but also to come down upon the small Greek force guarding the Pass of Thermopylae.