Very few of the Greeks were either slain or wounded; and it seemed as if the further advance of a million of men was to be stopped by a force less than a hundredth part of their number.
But now information reached Xerxes which completely changed the face of affairs.

There was a rough mountain-path leading from Trachis up the gorge of the Asopus and across Callidromus to the rear of the Greek position, which had been unknown to the Greeks when they decided on making their first stand at Thermopylae, and which they only discovered when their plans no longer admitted of alteration.

It was, perhaps, not much more than a goat-track, and apparently they had regarded it as scarcely practicable, since they had thought its defence might be safely entrusted to a thousand Phocians.

Xerxes, however, on learning the existence of the track, resolved at once to make trial of it.

His Persian soldiers were excellent mountaineers.