What was the main purpose of the battle of Thermopylae

The purpose of this battle is to hold the Persians fromadvancing so that the Athenians had enough time to evacuate to theisland of Salamis.It was clearly a suicide mission.Another view:The Athenians had known about the impending invasion for monthsand had plenty of time to evacuate their families whom they sentsouth to the Peloponnese cities for refuge. The pass was held topush the Persians to outflank the position by sea, and the combinedGreek navies lay in wait in the nearby strait of Artemesion todefeat them in a sea battle, and eliminate the amphibious threat totheir cities. Unfortunately the Persians won the sea battles overthree days. The blocking of the Thermopylae Pass had no furtherpurpose so the blocking force was withdrawn. The Spartan 300 plustheir 2,100 light and the Thespian 1,400 stayed behind to cover theretreat of the other 7,000 city contingents and were killed – anoble sacrifice to protect their allies.