The land-force at Thermopylae consisted chiefly of Peloponnesians; its numbers were as follows:--three hundred heavy-armed Spartans; five hundred Tegeans; five hundred Mantinaeans; one hundred and twenty Orchomenians; one thousand from the other states of Arcady; two hundred from Phlius; eighty from Mycenae.
Boeotia contributed seven hundred Thespians, and four hundred Thebans; the last had been specially selected by Leonidas, the Spartan chief, because of the general suspicion that the Thebans were attached to the Medes, and he desired, therefore, to approve them as friends, or know them as foes.

Although the sentiments of the Thebans were hostile, says Herodotus, they sent the assistance required.

In addition to these, were one thousand Phocians, and a band of the Opuntian Locrians, unnumbered by Herodotus, but variously estimated, by Diodorus at one thousand, and, more probably, by Pausanias at no less than seven thousand.
The chief command was intrusted, according to the claims of Sparta, to Leonidas, the younger brother of the frantic Cleomenes [62], by a different mother, and his successor to the Spartan throne.
There are men whose whole life is in a single action.

Of these, Leonidas is the most eminent.

We know little of him, until the last few days of his career.