Excerpts from Books and Wikipedia
"The Battle of Plataea was the final land battle during the second Persian invasion of Greece. It took place in 479 BC near the city of Plataea in Boeotia, and was fought between an alliance of the Greek city-states (including Sparta, Athens, Corinth and Megara), and the Persian Empire of Xerxes I. The previous year the Persian invasion force, led by the Persian king in person, had scored victories at the battles of Thermopylae and Artemisium and conquered Thessaly, Boeotia, Euboea and Attica. However, at the ensuing Battle of Salamis, the Allied Greek navy had won an unlikely but decisive victory, preventing the conquest of the Peloponnesus. Xerxes then retreated with much of his army, leaving his general Mardonius to finish off the Greeks the following year. In the summer of 479 BC the Greeks assembled a huge (by ancient standards) army and marched out of the Peloponnesus. The Persians retreated to Boeotia and built a fortified camp near Plataea. . . . While attempting a retreat after their supply lines were disrupted, the Greek battle line fragmented. Thinking the Greeks in full retreat, Mardonius ordered his forces to pursue them, but the Greeks . . . halted and gave battle . . ."