The Athenian and Eretrian assistance towards the Ionian city-states at Minor Asia and their successful revolt against the Persian rule was the cause of the Persian expedition of Mardonius against Athens and Eretria in the spring of 492 B.C. Mardonius easily brought under the Persian rule the Thrace and most of the Macedonian region. Two years later A very well equipped Persian expeditionary force under the leadership of Datis and Artapherne (spring 490) which also included Greek forces from Ionia and Aioleda. The first eminent general, Datis, was leading the ground forces (infantry and cavalry) and, Artapherne, son of the like-name Satrap, was leading the naval forces.
The Persian army, for cutting Athens from its allies and colonies, advanced and captured the islands of Naxos, Kareston and Eretria after treason by the part of the Persian-friendly side. The military assistance of the Athenians towards the Eretrians (4,000 Chalkides and Athenians) was forced to leave the island because of the strong argumentation and division in between the Eretria’s citizens. As a result the city-state was raised into dust, including the temples and shrines, and its survivors were leaded to Darius who send them to settle at Arderika, 200 stadiums from Sousa. The conquered Eretria became the stronghold and support ground of the expeditionary Persian force. The next target seemed to be Attica and Athens itself.
Soon the Persian force landed in the plain of Marathon with 20,000 infantry and unknown number of cavalry (Herodotus does not mentions any of the actions taken by the Persian cavalry). With the news of the Persian force at Marathon, the Athenians asked the assistance of the only city-state able to help, the Spartans (Thebes was already at the side of the Persian foe). Miltiades, the Athenian general, request help by the Spartans by sending the messenger Pheidepides who cried “μὴ περιιδεῖν πόλιν ἀρχαιοτάτην ἐν τοίσιν Ἕλλησι δουλοσύνη περιπεσοῦσαν προς ἀνδρὼν βαρβάρων.” Regardless, though, that the Spartans agreed to assist – and had sent an elite unite – Athens against the Persians, they asked for an additional time before any military actions, something that Athenians had none. The Spartan lack of immediate action was based upon two reasons, according to the more realistic account of Plato and not as Herodotus claimed: a) the fear towards the Helotes and b) the need of the deployment of a special unite which would efficiently pass through enemy ground such of the Argians (Plat.Laws, iii.698d and 698e). Miltiades did not wait for long, and he gathered his force of 10,000 men, including 1,000 Plataieis, at the Northeast rocky hill of the Agrielekiou – part of the Mt. Pentelikon.
