Our main sources for early Hoplite warfare come from the writings of Herodotus, who was born in the Greek city of Halicarnassus, on the southwest coast of Asia Minor, in 484 bc. He was an Ionian Greek who traveled widely and lived for a while in Athens, before settling in Thurii, a Greek colony in southern Italy. He died about 424 bc.
We also get information from Thucydides, an Athenian who wrote of the Pelopponnesian Wars. We can also find references in the works of several of the Greek playwrights' material on Hoplite warfare. We can find an account of the Second Persian Invasion in the play "Persae" by Aeschylus, who fought at Marathon during the First Persian Invasion, and possibly took part in the Second Persian War also. Apart from these sources, we must rely on later writers for this time period.
Cyrus the Great, through a series of daring attacks upon his neighbors, blended with masterful diplomacy, had created the Persian Empire in a very short period of time. From his base territory around Susa, situated just east of the Persian Gulf, Cyrus quickly defeated and annexed the Medes. From there, he quickly turned his attention to the Lydians in Asia Minor, conquering Croesus, the Lydian King, and taking Sartus, the Lydian capital.
Cyrus then divided his Empire into several provinces governed by Satraps. The Aegean Coast was soon subjugated by Haspagus, while Cyrus concentrated upon the capture of Babylon in the east. Shortly after this, Cyrus met his death fighting the northern barbaric tribes. His son, Cambyses, sometimes called the Mad, conquered and added Egypt to the Empire before he was overthrown by a usurper, who ruled for a short period, until the usurper was in turn overthrown by Darius, who was of the royal Achaemenid family. Darius reorganized the Empire into 20 satrapies. Darius decided to expand his Empire into southeast Europe, and led his armies in an invasion across the Bosphorus, and even northward beyond the Danube. In battles with the Scythians, his armies fared badly, and the Persian force likely would have been surrounded and destroyed if not for the Ionian Greeks contingent, which stood fast and guarded the Danube bridgehead while Porius withdrew his forces.
From this, the Ionians decided the time was ripe for a revolt against Persian rule. An envoy was sent from Miletus, the main city of the Ionians, to mainland Greece, petitioning the Greek city-states for armed aid against the Persians. The Spartans refused aid, but the Athenians chose to contribute twenty ships to the cause of Greek independence in the east. Eretria, on the island of Euboa, also sent five ships as aid. At first the revolt of the Ionian cities was successful, with the Greeks marching into and burning Sartus, where the Persian Satrap had his capital. But this success was short-lived, as the Persians retaliated and the Greek fleet was destroyed at the Battle of Lade in 494 bc. The city of Miletus was destroyed by the Persians, and its inhabitants were massacred or enslaved.
Due to the aid given to the Ionians by Athens and the other city-states of the mainland, Darius prepared a punitive strike against the Greek mainland. His fleet, under the command of his son-in-law, set sail in 492 bc., sailing along the northern Aegean coastline. The fleet was badly damaged in a storm off the coast of Mount Athos, forcing Darius to send a second fleet.
The second fleet, under new commanders, crossed the central Aegean, hopping from island to island. Eretria was quickly captured and destroyed by the Persians. The Persians then crossed to the northwest coast of Attica, and disembarked on the plain of Marathon, from which the road ran south straight to Athens. The road was the only practical route south, as it skirted Mount Pentelicus. At Marathon, the Persians found an Athenian army deployed across the road, blocking their route. The Athenian army, in a desperate battle, routed the Persians on the plain. The surviving Persians and those who had not been committed to the battle were then transported around Cape Sunium by their fleet to attack Athens from the Saronic Belf. But they found that the victorious Athenian army had arrived back from Marathon and had manned the defenses of Athens shortly before the Persians arrived. The Persian fleet returned to Asia Minor.
The Persian Invasion and the Battle of Marathon