How many days did the main battle at Thermopylae last?

The main battle at Thermopylae lasted three days. In 480 BC, King Leonidas and a Greek coalition held the narrow pass against the invading Persian army led by Xerxes I.

The Greeks arrived before the fighting began and initially held the pass for longer than three days overall. The Persian army spent time deploying, while the direct fighting took place over three days. On the first two days, the defenders repelled repeated Persian attacks, including assaults by the elite Immortals.

The turning point came when Ephialtes revealed the Anopaea mountain path, allowing Persian troops to outflank the Greek position. On the third day, Leonidas dismissed most of the allied force but remained with the Spartans, Thespians, Thebans, and others. The defenders were eventually overwhelmed, opening the route into central Greece.

A common mix-up is saying Thermopylae lasted only one day because the famous final stand dominates popular retellings. Another is counting the entire defensive operation rather than the three days of direct battle.