[2] The Boeotian-Greek city of Thebes had paid tokens of submission to a herald of the Persian King Xerxes while his army was still crossing through Macedon toward Greece, as had most of the other Boeotians, the Thessalians, and numerous other northern Greek tribes.
[3] The Spartan king Leonidas, therefore wary of Theban loyalty, pressed for Thebes to send troops to join him to test whether they would honor or refuse the Greek alliance against the Persians.
Thebes responded by sending 400 hoplites, led by Leontiades, to join the Greek coalition at the mountain pass of Thermopylae.
[5] When the Persians learned on the second night of a route by which they could encircle the Greek position, and Leonidas responded by dismissing most of the Greek army from the pass, Leontiades's Thebans were the only group which Leonidas compelled to remain there with his Spartans (although the Thespians led by Demophilus stayed as well, refusing the order to withdraw).
But when the Persian encirclement of the pass was completed and the Spartans and Thespians retreated to the position of their final stand, Leontiades and the Thebans took the opportunity to split off and rush forward to surrender.