During the Persian invasion of 480  Thespiae's ability to field a substantial force of hoplites had changed. Thespiae and Thebes were the only Boeotian cities to send a contingent to fight at Thermopylae, Thespiae sending a force of 700 hoplites who remained to fight beside the Spartans on the final day of the battle. In 1997, the Greek government dedicated a monument to the Thespians who fell alongside that of the Spartans. After the battle, Thebes was the final Boeotian state to side with the Persians, and in doing so they denounced both Plataea and Thespiae to Xerxes I as the only Boeotian states to side with the Greeks. After the city was burned down by Xerxes, the remaining inhabitants furnished a force of 1,800 men for the confederate Greek army that fought at Plataea.