What did Spartans do at Thermopylae pass?

As part of a Greek blocking force, they helped hold the pass for three days to make the Persians try to break through by turning the bottleneck by sea. The Greek navies were waiting offshore to pounce on the Persian navy to try to eliminate it and its threat to the Greek cities. As it turned out, the Greek navies were defeated and withdrew to try again at Salamis. The land blocking force at Thermopylae, its mission now invalidated, withdrew. The Spartan contingent of 300 heavy infantry and 2,100 light infantry, together with the Thespian contingent, remained holding the pass to allow the other city contingents to escape to the walls of friendly cities before the Persian cavalry broke through and rode them down in open countryside. They were killed to a man, a noble sacrifice to save their comrades.