Fearing the Greeks might attack the bridges across the Hellespont and trap his army in Europe, Xerxes now retreated with much of the Persian army back to Asia, though nearly all of them died of starvation and disease on the return voyage. He left a hand-picked force, under Mardonius, to complete the conquest the following year. However, under pressure from the Athenians, the Peloponnesians eventually agreed to try to force Mardonius to battle, and they marched on Attica. Mardonius retreated to Boeotia to lure the Greeks into open terrain, and the two sides eventually met near the city of Plataea. At the Battle of Plataea, the Greek army won a decisive victory, destroying much of the Persian army and ending the invasion of Greece. Meanwhile, at the near-simultaneous naval Battle of Mycale, they also destroyed much of the remaining Persian fleet, thereby reducing the threat of further invasions.