Agis III (d.330 BC) was a Spartan king who attempted to revive his city's fortunes, but who was killed during a revolt against Alexander the Great.
He was the elder son of Archidamus III, who died while fighting in Italy in 338 BC. His father had failed to stop the rise of Philip II of Macedonia, and Agis was faced with his son Alexander the Great. In 333 Agis III took a single trireme to Pharnabazus and Autophradates, the Persian commanders in the Aegean, in an attempt to raise money and troops. He was given 30 talents and 10 triremes, but the news then arrived of Alexander's great victory at Issus and the planned uprising was put on hold. Agis probably used the triremes to gain control of Crete.
Over the next couple of years Agis recruited 8,000 Greek mercenaries who had survived the Persian defeat at Issus. In 331, while Alexander's regent in Greece Antipater was dealing with a revolt in Thrace, Agis began his own uprising. He defeated Corragus, the Macedonian commander in the Peloponnese, and then besieged Megalopolis.
Antipater ended the fighting in Thrace and moved south to deal with the new threat. According to Diodorus the Greeks had around 20,000 men, mainly from the north and the Peloponnese, while Antipater had 40,000 men.
The decisive battle came near Megalopolis. Agis was wounded during the fighting, but the Spartan troops held their position until their Greek allies were forced to retreat. The surviving Spartans then withdrew back to the city. Agis was said to have sacrificed himself during the retreat, ordering his escorts to leave while he won them time to escape. The Spartans and their allies were said to have lost 5,300 men, Antipater 3,500.