By place

Greece

• Darius I sends an expedition, under Artaphernes and Datis the Mede across the Aegean to attack the Athenians and the Eretrians. Hippias, the aged ex-tyrant of Athens, is on one of the Persian ships in the hope of being restored to power in Athens.
• When the Ionian Greeks in Asia Minor rebelled against Persia in 499 BC, Eretria joined Athens in sending aid to the rebels. As a result, Darius makes a point of punishing Eretria during his invasion of Greece. The city is sacked and burned and Darius enslaves its inhabitants. He intends the same fate for Athens.
• September 12 — The Battle of Marathon takes place as a Persian army of more than 20,000 men is advised by Hippias to land in the Bay of Marathon, where they meet the Athenians supported by the Plataeans. The Persians are repulsed by 11,000 Greeks under the leadership of Callimachus and Miltiades. Some 6,400 Persians are killed at a cost of 192 Athenian dead. Callimachus, the war-archon of Athens, is killed in the battle. After the battle, the Persians return home.
• Before the Battle of Marathon, the Athenians send a runner, Pheidippides, to seek help from Sparta. However, the Spartans delay sending troops to Marathon because religious requirements mean they must wait for the full moon.
• According to a much later tradition, after the Battle of Marathon, Pheidippides, who has already run 140 miles to Sparta and return over five days and nights, runs 26.2 miles (40 kilometres) from Marathon to Athens to carry the news of the victory. His last words before collapsing and dying are: "Rejoice, we're victorious."
• Hippias dies at Lemnos on the journey back to Sardis after the Persian defeat.
• Cleomenes I is forced to flee Sparta when his plot against Demaratus is discovered, but the Spartans allow him to return when he begins gathering an army in the surrounding territories. However, by this time he's become insane, and the Spartans put him in prison. Shortly after, he commits suicide. He is succeeded as King of Sparta by a member of the Agiad house, his half-brother, Leonidas.
• The Athenians begin the building of a temple to Athena Parthenos (approximate date).

  Births

• Empedocles, Greek philosopher (d. c. 430 BC)
• Zeno of Elea, Greek philosopher (d. c. 430 BC)

Deaths