 This time Mardonius could not persuade Xerxes, but when Xerxes left he did become governor of those parts of Greece that had been conquered by the Persians.He subdued Macedon, ruled at that time by King Alexander I, but Alexander himself gave valuable information about Mardonius' plans to the Athenians, saying that, as a Greek, he could not bear to see Greece defeated.After the first part of the campaign directly under the orders Xerxes I, Mardonius remained in Greece with 300,000 elite troops, who fought in the last stages of the war, destroying Athens, but being finally vanquished at the Battle of Platea