After the naval defeat of Salamis, Xerxes realised he could no longer hold Athens without naval supremacy - logistics became impossible. So he began a withdrawal, leaving Mardonius with about 100,000 men in northern Greece.
The Spartan King Pausanias leading the main Greek army of about 80,000 caught up with the Persians along the line of the Asopus River and formed for battle in three phalanxes, Athenians to the left, Spartans on the right, allied Greeks in the centre.
For 8 days both sides faced each other, while raiding took place by Persian cavalry in the Greek rear, cutting supply lines and disrupting water supply. Thus Pausanias decided to withdraw to a more defensible position but in the dark, the Greeks got separated from each other. Seeing this Mardonius attacked the Spartans, but they stood their ground and counter-attacked, killing Mardonuis himself. Meanwhile the Athenians fought hard and were almost enveloped and destroyed, but the allies returned to the field just in time to intercept the Persian cavalry and turn the tide. The Persians were forced back to and into the river, suffering terrible losses. The invasion was over.