The First Persian war began when Darius became Emperor of Persia. The Persian Empire encompassed a large geographic area including large portions of Anatolia (present day Turkey.) A substantial number of Greek colonies, including Ephesis and Miletus were within the influence of Persia and ruled by Persian satraps. Although the Persians tended to be tolerant of other cultures within their Empire, the Greeks in Anatolia resented Persian rule, and staged a series of revolts. The Persian Emperor, Darius, put down the revolts in 493 B.C.E., but was angered that Athens, the Greek City State, had sent ships to aid the rebelling colonies. Darius sent ships to attack Athens in 490 B.C.E. to punish that city-state, and prevent further Greek influence in Persian affairs. Interestingly, Sparta was preoccupied with attempts to keep its Helot adversaries under control and did not participate in the first War; however the Greeks from Athens were able to defeat the Persians despite being outnumbered. Marathon was the decisive battle which ended the war.
Herodotus reports that a runner, Phidippides was sent to Sparta to ask for help but to no avail. Following the battle of Marathon, he was again dispatched to deliver word of the victory to Athens which he did; however the strenuousness of the ordeal was too much for him, and he collapsed and died shortly thereafter. It is his heroic effort that has given the name of "Marathon" to a long ordeal.