Perdiccas III (r.368/7-360/59 BC) was a king of Macedon who was killed in battle against the Illyrians, leaving the throne to his brother Philip II.
Perdicass was the middle son of Amyntas III, a rare example of a Macedonian monarch with a lengthy reign. After Amyntas's death he was succeeded by his oldest son Alexander II, but he only ruled for a year or two before he was assassinated by his brother-in-law Ptolemy Alorites. According to Diodorus Ptolemy ruled as king of Macedon, but he probably only ever held the post of regent, working alongside his mother-in-law and possible lover Eurydice.
Aeschines, in his Speech on the Embassy, gives the Athenian general Iphicrates credit for helping Perdiccas keep his throne. Pausanias, a rival from a different branch of the royal family, had gathered support outside Macedon and had captured Anthemon, Therma and Strepsam and had the support of a sizable faction within the kingdom. Perdiccas's mother Eurydice was said to have taken Perdiccas and his young brother Philip (the future Philip II) to Iphicrates to plead for his support. In response Iphicrates drove Pausanias out of Macedon, and probably made or supported Ptolemy Alorites (said to have been Eurydice's lover) as regent of Macedon.
Plutarch, in his life of the Theban general Pelopidas, records a different incident. After murdering Alexander II of Macedon, Ptolemy seized power. Pelopidas, who was in Thessaly as an ambassador, received calls for help from Alexander's friends. He raised a force of mercenaries and advanced into Macedon. Ptolemy managed to bribe the mercenaries, but still submitted to Pelopidas, who had an impressive reputation. Ptolemy agreed to act as the regent for Perdiccas.
For the first three years of his reign Ptolemy served as regent for the young king, but in 364 the king had his regent murdered and took control in his own right. We don’t know much about his reign, although we do know that he probably supported Amphipolis in its long struggle for independence from Athens. He was also a patron of scholars, and supported the philosopher Euphraeus.
Perdiccas's reign ended in a great crisis for Macedon. The king was engaged in a war with the Illyrians, but he was killed and defeated in battle by King Bardylis of the Dardanians. According to Diodorus the Macedonians lost around 4,000 men in the battle, and the survivors were no longer willing to fight on. The Paeonians, northern neighbours of Macedon, also bean a series of raids. Perdiccas had a young son Amyntas, but in the crisis he was probably passed over in favour of Perdiccas's younger brother Philip II.