Mardonius Mardonius ( , ; died 479 BC ) was a leading Persian military commander during the Persian Wars with Greece in the early 5th century BC . Early years . Mardonius was the son of Gobryas , a Persian nobleman who had assisted the Achaemenid prince Darius when he claimed the throne . The alliance between the new king and his friend was cemented by diplomatic marriages : Darius married Gobryas ' daughter , and Gobryas married Darius ' sister . Furthermore , Mardonius married Darius ' daughter Artozostra . Thus Darius the Great was simultaneously Mardonius ' uncle , father - in - law , and half - brother - in - law . Persian Wars with the Greeks . Darius appointed Mardonius as one of his generals and , after the Ionian Revolt , sent him in 492 BC to punish the Greek city - state of Athens for assisting the Ionians . On his way to Athens , he used his army in the Ionian cities to depose the Greek tyrant s and set up democratic governments , an action which surprised the Greeks at that time . Historians consider that he may have taken this action so that the Ionians would not revolt a second time after the Persian army had passed through . His fleet and army then passed across the Hellespont . Mardonius first attacked Thasos , a Greek island which possessed gold mines . It became a tributary of the Achaemenid empire . The navy and the army continued onto Macedonia , which was soon added to the Persian Empire . However , after these victories , Mardonius ’ fleet was destroyed in a storm off the coast near Mount Athos . According to Herodotus , the Persians lost 300 ships and 20 , 000 men . Around this time , Mardonius was commanding the army in a battle in Thrace . While Mardonius was wounded in the battle , he was victorious . Nevertheless , the loss of the fleet meant that he had to retreat back into Asia Minor . He was relieved of his command by Darius , who appointed Datis and Artaphernes to lead the invasion of Greece in 490 BC , and though they were subsequently successful in capturing Naxos and destroying Eretria , they were later defeated at the Battle of Marathon . Mardonius came back into favour under Darius ' successor Xerxes I , Mardonius ' cousin and brother - in - law . Xerxes was at first not interested in renewing the war with Greece , but Mardonius repeatedly tried to convince him that he must avenge Darius ' defeat . This view was opposed by another of Xerxes ’ advisors , Artabanus , who urged more caution in the matter . Herodotus , who portrays Mardonius as a somewhat evil adviser ( as opposed to a number of other good advisers whose arguments are never followed ) , says that Mardonius simply wanted to become satrap ( governor ) of Greece and had a love for ' mischief and adventure ' . He was present at the Battle of Thermopylae , and after the Persian defeat at the Battle of Salamis , he attempted to convince Xerxes to stay and fight yet another campaign . 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 . Then Mardonius sacked Athens , which had been deserted before the Battle of Salamis . He offered to return Athens and help rebuild the city if the Athenians would accept a truce , but the Athenians rejected the truce and prepared for another battle . Mardonius prepared to meet them at Plataea , despite the opposition from another Persian commander , Artabazus , who , like Artabanus , did not think that the Persian army could automatically defeat the Greeks . Mardonius was killed in the ensuing battle by the Spartans ( see Battle of Plataea ) . It is claimed by Herodotus and Plutarch a Spartan called Arimnestus killed Mardonius with a stone . This led to his army breaking up .