Battle of Marathon - Wikipedia

September 12, 490 BC is the traditional date of the Battle of Marathon where a small Athenian force defeated the Persian Empire. From the article:

"The first Persian invasion was a response to Athenian involvement in the Ionian Revolt, when Athens and Eretria had sent a force to support the cities of Ionia in their attempt to overthrow Persian rule. The Athenians and Eretrians had succeeded in capturing and burning Sardis, but they were then forced to retreat with heavy losses. In response to this raid, Darius swore to burn down Athens and Eretria. According to Herodotus, Darius had his bow brought to him and then shot an arrow "upwards towards heaven", saying as he did so: "Zeus, that it may be granted me to take vengeance upon the Athenians!". Herodotus further writes that Darius charged one of his servants to say "Master, remember the Athenians" three times before dinner each day.[5]

At the time of the battle, Sparta and Athens were the two largest city-states in Greece. Once the Ionian revolt was finally crushed by the Persian victory at the Battle of Lade in 494 BC, Darius began plans to subjugate Greece. In 490 BC, he sent a naval task force under Datis and Artaphernes across the Aegean, to subjugate the Cyclades, and then to make punitive attacks on Athens and Eretria. Reaching Euboea in mid-summer after a successful campaign in the Aegean, the Persians proceeded to besiege and capture Eretria. The Persian force then sailed for Attica, landing in the bay near the town of Marathon. The Athenians, joined by a small force from Plataea, marched to Marathon, and succeeded in blocking the two exits from the plain of Marathon. The Athenians also sent a message asking for support to the Spartans. When the messenger arrived in Sparta, the Spartans were involved in a religious festival and gave this as a reason for not coming to aid of the Athenians.

The Athenians and their allies chose a location for the battle, with marshes and mountainous terrain, that prevented the Persian cavalry from joining the Persian infantry. Miltiades, the Athenian general, ordered a general attack against the Persian forces, composed primarily of missile troops. He reinforced his flanks, luring the Persians' best fighters into his center. The inward wheeling flanks enveloped the Persians, routing them. The Persian army broke in panic towards their ships, and large numbers were slaughtered. The defeat at Marathon marked the end of the first Persian invasion of Greece, and the Persian force retreated to Asia. Darius then began raising a huge new army with which he meant to completely subjugate Greece; however, in 486 BC, his Egyptian subjects revolted, indefinitely postponing any Greek expedition. After Darius died, his son Xerxes I restarted the preparations for a second invasion of Greece, which finally began in 480 BC.

The Battle of Marathon was a watershed in the Greco-Persian wars, showing the Greeks that the Persians could be beaten; the eventual Greek triumph in these wars can be seen to begin at Marathon. The battle also showed the Greeks that they were able to win battles without the Spartans, as they had heavily relied on Sparta previously. This victory was largely due to the Athenians, and Marathon raised Greek esteem of them. Since the following two hundred years saw the rise of the Classical Greek civilization, which has been enduringly influential in western society, the Battle of Marathon is often seen as a pivotal moment in Mediterranean and European history."