The Battle of Marathon took place in 490 BC, and is probably the best known battle of the Persian Wars, though much of its significance is mythic rather than military. The main source is the Histories of Herodotus, who wrote many years after the battle, but his account is supplemented by various later historians, who add important details. For instance, estimates of the relative size of the Greek and Persian armies appear in the work of the Roman historian Cornelius Nepos, who says that there were 10,000 Greeks (9,000 of them Athenians) and 210,000 Persians, 10,ooo of whom were cavalry.
The Persians had come to Greece to punish the Greeks—the Athenians in particular—for their aid to the cities of Ionia in their rebellion against Persia. Before this event, the Persians had shown little interest in Greece. When the two armies met on the plain at Marathon, it appears that the Greeks, commanded by Miltiades, charged straight at the Persians. The marshy ground prevented the Persians from using their cavalry, and a large part of the Persian infantry was soon trapped between the Greek army's strong flanks. When this became clear, the Persians ran for their ships, and many died in the marshes.
The Battle of Marathon put an end to the first Persian invasion of Greece. Although Darius, the Persian King, planned to renew the invasion, he was prevented from doing so by a revolt in Egypt. However, his son Xerxes, launched the second Persian invasion in 480 BC, meaning that the Battle of Marathon, despite being an important Greek victory, was not decisive. The Battle of Plataea in 479 BC was the most strategically significant victory for the Greeks in repelling the Persians from Attica.