The Greco-Persian Wars

The Persian Empire, the largest on earth, moved to punish the Greek city-states for aiding a revolt against it. In 490 BCE Darius sent a force that Athens beat at Marathon; ten years later his son Xerxes returned with an army so large ancient writers gave up counting. Three hundred Spartans and their allies under Leonidas held the pass at Thermopylae long enough to matter and died there; Athens was evacuated and burned. Then the Athenian general Themistocles lured the Persian fleet into the narrow strait at Salamis, where its numbers became a liability, and destroyed it. The Greeks finished the invasion at Plataea the next year. Heavily armored citizen-hoplites and nimble triremes had beaten a subject levy — and reach had outrun grip even for the mightiest empire on earth.