Themistocles was the architect of Athens' navy. He convinced the Athenians to build a serious fleet in 483 B.C. when they had a surplus of funds. Their fleet, in turn, helped save Greece when the Persians invaded in 480. Indeed, Greece would almost certainly have been defeated w/o Athens, which means that classical Athens as we know it--the radical democracy, art, philosophy and literature, the buildings of the Acropolis--would not have happened.