(Ἀρριδαῖος) or ARIDAEUS (Ἀριδαῖος).
1. A half-brother of Alexander the Great, son of Philip and a female dancer, Philinna of Larissa, was of imbecile understanding, which was said to have been occasioned by a potion administered to him when a boy by the jealous Olympias. Alexander had removed Arrhidaeus from Macedonia, perhaps through fear of his mother Olympias, but had not entrusted him with any civil or military command. He was at Babylon at the time of Alexander's death, B. C. 323, and was elected king under the name of Philip. The young Alexander, the infant son of Roxana, who was born shortly afterwards, was associated with him in the government. [ALEXANDER IV., p. 122b.] In the following year, B. C. 322, Arrhidaeus married Eurydice [EURYDICE], and was from this time completely under the direction of his wife. On their return to Macedonia, Eurydice attempted to obtain the supreme power in opposition to Polysperchon. Roxana and her infant son fled to Epeirus, and Olympias induced Aeacides, king of Epeirus, to invade Macedonia in order to support Polysperchon. Aeacides was successful in his undertaking : Arrhidaeus and Eurydice were taken prisoners, and put to death by order of Olympias, B. C. 317. In the following year, Cassander conquered Olympias, and interred the bodies of Arrhidaeus and Eurydice with royal pomp at Aegae, and celebrated funeral games to their honour. (Plut. Alex. 77; Dexippus, apud Phot. Cod. 82; Arrian, apud Phot. Cod. 92; Justin, 9.8, 13.2, 14.5; Diod. 18.2, 19.11, 52; Paus. 1.6.3, 25. §§ 3, 5, 8.7.5; Athen. 4.155.)