In Plutarch's report, he became both physically and mentally disabled following a poisoning attempt by Philip II's wife, Queen Olympias, who wanted to eliminate a possible rival to her son Alexander. However, this may just be malicious gossip, and there is no evidence that Olympias really caused her stepson's condition. Alexander was very fond of him, and took him on his campaigns, both to protect his life and to ensure he would not be used as a pawn in a challenge for the throne. After Alexander's untimely death in Babylon, Arrhidaeus was proclaimed king by the Macedonian army in Asia. However, he was a mere figurehead, and a pawn of the powerful generals, one after the other. His reign and his life did not last long.
He was at Babylon at the time of Alexander's death, the 11 June 323 BC. A succession crisis erupted: Arrhidaeus was the most obvious candidate, but he was mentally unfit to rule. A conflict exploded between Perdiccas, leader of the cavalry, and Meleager, who commanded the phalanx: the first wanted to wait to see if Roxana, Alexander's pregnant wife, would deliver a male baby, while the second objected that Arrhidaeus was the closest relative living and so should be chosen king. Meleager was killed, and a compromise was engineered: Arrhidaeus would become king with the name of Philip, and he would be joined by Roxana's son as co-sovereign should he prove a male, as he did, and joined his uncle with the name of Alexander. It was immediately decided that Philip Arrhidaeus would reign, but not rule: this was to be the prerogative of the new regent, Perdiccas.
When news arrived in Macedon that Arrhidaeus had been chosen as king, Cynane, a daughter of Philip II, matured the design to travel to Asia and offer the new king her daughter Eurydice for wife. This move was an obvious affront to the regent, whom Cynane had completely bypassed: to prevent the move Perdiccas sent his brother Alcetas to kill Cynane, but reactions among the troops generated by this murder was such that the regent had to give up and accept the marriage. From that moment on Philip Arrhidaeus was to be under the sway of his bride, a proud and determined woman bent on substantiating her husband's power.
Eurydice's chance came when the first war of the Diadochi sealed the fate of Perdiccas, making a new settlement necessary; settlement that was made at Triparadisus in Syria in 320 BC. Eurydice moved deftly enough to obtain the removal of the first two designed regents, Peithon and Arrhidaeus, but was powerless to block the too powerful Antipater: the latter was made new regent and Philip Arrhidaeus and his wife were forced to follow him to Macedon.
The regent died of natural causes the following year, nominating as his successor not his son Cassander, but a friend of his, Polyperchon. Cassander's refusal to accept his father's decision sparked the second war of the Diadochi, in which Eurydice saw once again a chance to free Philip from the control of the regent. An opportunity presented itself in 317 BC, when Cassander expeled Polyperchon from Macedon: Eurydice immediately allied herself with him and made her husband nominate him new regent, and Cassander reciprocated by leaving her in full control of the country when he left to campaign in Greece. Another important designation was that of Eumenes as new commander of the Macedonian forces in Asia, dismissing in this way Polyperchon's strongest ally, Antigonus Monophthalmus.
But all this was to prove exceedingly volatile: that same year (317) Polyperchon and Olympias, allied with the king of Epirus Aeacides, invaded Macedon, while the Macedonian troops refused to fight the son of Alexander, whom the invaders had brought with them. Philip and Eurydice had no choice but to escape, only to be captured at Amphipolis and thrown into prison. It soon became clear that Philip was too dangerous to be left alive, as many enemies of Olympias saw him as a useful tool against her, and so on December 25 317 BC she had him executed, while his wife was forced to commit suicide.
The following year, when Cassander reconquered Macedon and avenged Philip's death, he interred the bodies of Philip and Eurydice with royal pomp at Aegae, and celebrated funeral games to their honour.
In 1977 important excavations were made near Vergina leading to the discovery of a two-chambered royal tomb, with an almost perfectly conserved male skeleton. Manolis Andronikos, the chief archaeologist on the ground and the majority of archaeologists, decided it was the skeleton of Philip II, but many have disputed this attribution and instead proposed it to be the remains of Philip Arrhidaeus.
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