223 BC

By place

Seleucid Empire

• The Seleucid king Seleucus III is assassinated in Phrygia by members of his army while on campaign against Attalus of Pergamon.
• Seleucus is succeeded by his younger brother, Antiochus III. From the previous administration, Antiochus III retains Hermeias as his chief minister, Achaeus as governor of Anatolia, and Molon and his brother Alexander as governors of the eastern provinces of Media and Persis.

  Roman Republic

• Gaius Flaminius is elected consul for the first time and, with Publius Furius Philus, he forces the Cisalpine Gauls to submit to Rome, creating the province of Cisalpine Gaul.

  Greece

• The Spartan king Cleomenes III destroys and burns the city of Megalopolis but the inhabitants are saved by Philopoemen who leads the defence of the city until the inhabitants can escape.
• The king of Macedonia, Antigonus III Doson, restores Macedonian influence in the Peloponnese for the first time in almost two decades. After signing alliances with the Achaeans, Boeotians, Thessalians and the Acarnanians, Antigonus invades the Peloponnese and drives the Spartans out of Argos, taking Orchomenus and Mantineia in the process.

  Persia

• King Diodotus II of Bactria is killed by a usurper, Euthydemus I, founder of the Greco-Bactrian Euthydemid dynasty.

  China

• The state of Qin conquers the state of Chu.