Thespiae contributed 700 soldiers who fought and died at Thermopylae. They were led by Demophilus, and their decision to remain alongside Leonidas became one of the clearest examples of collective sacrifice in the battle.
The Thespians came from Thespiae, a Boeotian city in central Greece. Unlike the Spartan contingent, which is often portrayed as fulfilling a military obligation under Leonidas, the Thespian troops are traditionally remembered as choosing to stay after the main Greek force was ordered to withdraw.
When the Persian army outflanked the Greek position, Leonidas dismissed most of the defenders. The remaining force included 300 Spartans and 700 Thespians, along with other troops mentioned in ancient accounts. The Thespians fought to the death during the final phase of the battle.
A common mix-up is to assume that every Greek defender at Thermopylae was Spartan. Sparta supplied the most famous unit, but the battle involved many allied city-states. The Thespians' role is especially significant because their entire contingent was reportedly lost, and their city was later destroyed by the advancing Persians.