Amyntas III (Greek: Ἀμύντας Γ΄; died 370 BC) was a Macedonian king of Macedon in 393 BC, and again from 392 to 370 BC. He was the son of Arrhidaeus and grandson of Amyntas, one of the sons of Alexander I. His most famous son is Philip II, father of Alexander the Great. He is historically considered the founder of the unified Macedonian state.
He came to the throne after the ten years of confusion which followed the death of Archelaus I. But he had many enemies at home; in 393 he was driven out by the Illyrians, but in the following year, with the aid of the Thessalians, he recovered his kingdom. Medius, head of the house of the Aleuadae of Larissa, is believed to have provided aid to Amyntas in recovering his throne. The mutual relationship between the Argeadae and the Aleuadae dates to the time of Archelaus.
To shore up his country against the threat of the Illyrians, Amyntas established an alliance with the Chalkidian League led by Olynthus. In exchange for this support, Amyntas granted them rights to Macedonian timber, which was sent back to Athens to help fortify their fleet. With money flowing into Olynthus from these exports, their power grew. In response, Amyntas sought additional allies. He established connections with Kotys, chief of the Odrysians. Kotys had already married his daughter to the Athenian general Iphicrates. Prevented from marrying into Kotys' family, Amyntas soon adopted Iphicrates as his son.
After the King's Peace 387 BC, Sparta was anxious to re-establish its presence in the north Greece. In 385 BC, Bardylis and his Illyrians attacked Epirus instigated and aided by Dionysius I of Syracuse, in an attempt to restore the Molossian king Alcetas I of Epirus to the throne. When Amyntas sought Spartan aid against the growing threat of Olynthus, the Spartans eagerly responded. That Olynthus was backed by Athens and Thebes, rivals to Sparta for the control of Greece, provided them with an additional incentive to break up this growing power in the north. Amyntas thus concluded a treaty with the Spartans, who assisted him to reduce Olynthus (379). He also entered into a league with Jason of Pherae, and assiduously cultivated the friendship of Athens. In 371 BC at a Panhellenic congress of the Lacedaemonian allies, he voted in support of the Athenians' claim and joined other Greeks in voting to help Athens to recover possession of Amphipolis.
With Olynthus defeated, Amyntas was now able to conclude a treaty with Athens and keep the timber revenues for himself. Amyntas shipped the timber to the house of the Athenian Timotheus, in the Piraeus.
Amyntas married Eurydice, daughter of Sirras of Lynkestis, circa 390. By her, Amyntas had three sons, all of whom became kings of Macedonia one after the other, and a daughter:
- Alexander II
- Perdiccas III
- Philip II, father of Alexander the Great.
- Eurynoe: According to Roman historian Justin, Eurynoe prevented Amyntas' assassination by her mother and her husband (thought to be Ptolemy of Aloros), who was also her mother's lover, by revealing the plan to her father. She is not referred again by any other source.
Justin also mentions that Amyntas had three sons by another wife, Gygaea (probably an Argead): Archelaus, Arrhidaeus and Menelaus. The fact that they did not try to take the throne before the 350s suggests that they were younger than Amyntas' children by Eurydice. They were ultimately eliminated by their half-brother Philip II because they had a claim to the throne.
Amyntas died at an advanced age, leaving his throne to his eldest son, Alexander II.