 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, Phocis, 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.