A bloody combat ensued, in which the Persians lost by far the greater number; but the ranks of the Greeks were gradually thinned, and they were beaten back step by step into the narrowest part of the pass, where finally they all perished, except the four hundred Thebans, who submitted and were made prisoners.
So terminated the first struggle on the soil of Greece, between the invaders and the invaded.

It seemed to promise that, though at vast cost, Persia would be victorious.

If her loss in the three days' combat was 20,000 men, as Herodotus states, yet, as that of her enemy was 4000, the proportionate advantage was on her side.
But, for the conquest of such a country as Greece, it was requisite, not only that the invader should succeed on land, but also that he should be superior at sea.

Xerxes had felt this, and had brought with him a fleet, calculated, as he imagined, to sweep the Greek navy from the Egean.

As far as the Pagasaean Gulf, opposite the northern extremity of Euboea, his fleet had advanced without meeting an enemy.