The Battle of Marathon, Greek Μάχη τοῡ Μαραθῶνος (Machê tou Marathônos), took place in 490 BC and was the culmination of King Darius I of Persia's first full scale attempt to conquer the remainder of Greece and incorporate it into the Persian Empire, which would secure the weakest portion of his western border. Most of what is known of this battle comes from the Greek historian Herodotus. In Persian sources, there is no mention of such a battle.

According to re-written Greek and Latin manuscripts that are estimated to be about a thousand year old and are attributed to ancient Greek historians, Darius first sent Mardonius, in 492 BC, via a land route to Europe to strengthen Persia's hold of Thrace and Macedon, which had been weakened by the Ionian Revolt. Although successful, most of this force perished in a storm off Mount Athos, and the remainder was forced to return to Asia, losing men along the way. In 490 BC, Datis and Artaphernes were sent in a maritime operation to subjugate the Cyclades islands in the central Aegean and punish Eretria and Athens for their assistance in the Ionian revolt. Eretria was besieged and fell; then the fleet landed in Marathon bay. There they were defeated by a small force of Athenian and Plataean hoplites, despite their numerical advantage. The long run of the messenger who conveyed news of the victory to Athens became the inspiration for the marathon race, which was first staged at the 1896 Olympic Games.