1.7.1 This Ptolemy, having-conceived-a-passion [erastheis] for Arsinoe, his full sister, married her, violating Macedonian custom [nomizomena] in doing so, but following that of his Egyptian subjects. Secondly he put to death his brother Argaios, who was, it is said, plotting against him; and it was he who brought down from Memphis the corpse [nekros] of Alexander. He put to death another brother also, son of Eurydikē, on discovering that he was creating disaffection among the Cypriotes. Then Magas, the half-brother of Ptolemy, who had been entrusted with the governorship of Cyrene by his mother Berenikē—she had borne him to Philip, a Macedonian but of no note and of lowly origin—induced the people of Cyrene to revolt from Ptolemy and marched against Egypt.

1.7.2 Ptolemy fortified the entrance into Egypt and awaited the attack of the Cyrenaeans. But while on the march Magas was informed that the Marmaridai, a tribe of Libyan nomads, had revolted, and thereupon fell back upon Cyrene. Ptolemy resolved to pursue, but was checked owing to the following circumstance. When he was preparing to meet the attack of Magas, he engaged mercenaries, including some four thousand Gauls. Discovering that they were plotting to seize Egypt, he led them through the river to a deserted island. There they perished at one another’s hands or by famine.

1.7.3 Magas, who was married to Apame, daughter of Antiokhos, son of Seleukos, persuaded Antiokhos to break the treaty that his father Seleukos had made with Ptolemy and to attack Egypt. When Antiokhos resolved to attack, Ptolemy dispatched forces against all the subjects of Antiokhos—he sent plunderers to overrun the lands of the weaker, and an army to hold back the stronger—so that Antiokhos never had an opportunity to attack Egypt. I have already stated how this Ptolemy sent a fleet to help the Athenians against Antigonos and the Macedonians, but it did very little to save Athens. His children were born of Arsinoe—not his sister, but the daughter of Lysimakhos. His sister who had wedded him happened to die before this, leaving no issue, and there is in Egypt a district called Arsinoites after her.