Pass of Thermopylae & Battlefield page 3
In ancient times the pass of Thermopylae was the only place on land for a sizable body of troops to pass from
Thessaly into southern Greece.
The pass is roughly 6,000 plus meters long and bottlenecks at both ends.
When the Greeks chose this pass they, according to Herodotus, 'were unaware of the mountain track by means of which the men who fell at Thermopylae were taken in the rear and were only informed of this fact after arrival by the people of Trachis." Leonidas, in fact posted 1000 Phocians on the track, called the Anopaia, to guard the rear but they were overrun by Xerxes' 2,000 plus crack troops "the Immortals"
The total Greek force is estimated at 7,300 men while Xerxes' Persian army was estimated at over 5,000,000, including camp followers
by Herodotus in book 7 of his Histories.
Modern scholars estimate it at a far more likely 300,000 strong. If you want to read the best account of the battle, Herodotus is the source.
Xerxes also had a huge navy which followed the army as close to the shore as it could get in a support role.
The Greeks knew this and since they had chosen Thermopylae as the battleground placed their fleet off Cape Artemision, Euboea to prevent the combined Persian fleet from sailing down the coast in support. One night while the Persian fleet was mosty beached or inshore a big storm came up and caused the loss of 400 ships. The Athenian Greeks, with 120 triremes, due to the wise council of Themistokles, had the biggest contingent of Greek naval forces. They avoided battle being greatly outnumbered.
As mentioned above, the combined Greek army was commanded by Leonidas King of Sparta and upon arrival at the pass ordered the repair of the existing defensive wall previously erected by the Phocians and took up position behind it in the center of the pass facing north.
