The Graham Phillips Website

Like Alexander, Arridaeus was the son of Philip II.  He was born a couple of years before his brother, to Philips’ first wife, a Greek woman named Philinna.  Macedonian custom allowed for a man to have more than one wife and the year after Arridaeus’ birth the king married Olympias, the daughter of a foreign king with whom he wished to cement an alliance.  One year after her marriage Olympias gave birth to her own son, Alexander, and from the very start there can be little doubt that she intended to make him Philips’ heir.

By the time he reached his late teens Arridaeus was widely thought unfit to succeed his father as he was considered weak-willed and feeble-minded.  The truth is that Arridaeus was a highly-intelligent, studious youth whose problem appears to have been epilepsy.   Displaying signs of military genius, Alexander was clearly a more suitable successor and Philip had officially named him as heir.  However, in 338 BC Philip divorced Olympias and she and Alexander were forced to leave the court.  Philip did not disinherit Alexander, but it may only have been a matter of time.  It appears that Olympias’ enemies argued that under supervision Arridaeus was still capable of becoming king.

Alexander and Arridaeus
Alexander and Arridaeus could not have been more opposite.  Alexander was handsome, athletic and a natural warrior, while his brother was sickly, timid and studious.
The ancient Sicilian historian Diodorus accuses Olympias and Alexander of assuring Alexander’s succession by orchestrating Philips’ assassination.   Alexander, however, must have been fond of his half-brother as he did not have him killed as he did other rivals for the throne. What, though, where Arridaeus’ feelings toward Alexander?  Did he harbor a bitter resentment against his brother for depriving him of the throne?  There are certainly reasonable grounds for suspicion.  During the remained of Alexander’s campaign Arridaeus remained behind in the west and did not see his brother again for eleven years.  When he finally did it was when he arrived unexpectedly in Babylon and, just a few weeks later, Alexander fell ill and died.