In 480 BCE.
Thermopylae was a very minor event in the 50-year Persian Wars. It failed to have any influence on the wars, and only later became symbolic of courage.
The Spartans did not 'follow' the Persians - they were part of a blocking force which delayed the Persian army for three days, and had no effect on the following two-year campaign which defeated the Persians at the battles of Salamis, Plataia and Mycale.
It was the Battle of Thermopylae in the Second Persian War. The Greeks won. Shortly after Thermopylae the Athenian Navy defeated the Persian Navy at Salamis, and in the next year the Persian Army was defeated by a combined Greek Army at Plataea.
Persia invaded mainland Greece in 480 to incorporate it into its empire. There was a minor delaying action at the Thermopylai pass as part of the two year invasion.
5th Century BCE - 480 BCE to be precise, and Thermopylae was not a war but rather a small battle in a 50-year war.
480 BC .
No, the Spartans did not ally with Persia, but they allied with the Athenians or Greeks, or else there would not have been the famous 300.The Spartans allied with the Athenians during the Thermopylae battle, the Persian wars and the peloponnesian war. After 3 years of war following the stand of the 300 the Spartans and Athenians defeated Persia!Sparta never allied with Persia!
The Battle of Thermopylae started and ended in 480BC.
The Persian Wars would have proceeded the same if the Spartans had not slowed the Persians at Thermopylae. The reason the Spartans wanted to hold up the Persian advance was to force a sea battle in the Artemisium Strait to destroy the Persian navy.The Persians won the sea battle, and it had to be refought later at Salamis. After the failure of the sea battle, the blocking force at Thermopylae was withdrawn. The battle had no effect on the outcome of the invasion.No difference whatsoever, the Persians simply moved on with a three day delay of no effect.
They lost one of their two kings and his bodyguard. They kept their army home defending their city. They agreed to continue the Greek strategy of trying to defeat the Persian fleet so that the southern Greek cities would not have to remain at home defending thier cities against threatened Persian amphibious attack, and could concentrate against the persian army, which they did the following year. As the sea battle at Artemesion which was precipitated by the holding of the pass at Thermopylai failed, there was little result from Thermopylai other than good propaganda after the war.
Thermopylai was a minor action in the two-year Persian invasion of mainland Greece, where a small combined force from the southern Greek city-states blocked the pass for three days before withdrawing.
It started and ended within three days in 480 BCE.