PTOLEMY III  . Euergetes I . (reigned 246-221), son of Ptolemy II. and Arsinoe I . At the beginning of his reign he reunited the Cyrenaica to Egypt by marrying Berenice the daughter and successor of Magas (who had died about 250) . At the same time he was obliged to open war on the Seleucid kingdom, where Antiochus II. was dead and his sister Berenice had been murdered, together with her infant son, by Antiochus's former wife, Laodice, who claimed the kingdom for her son Seleucus II . Ptolemy marched triumphantly into the heart of the Seleucid realm, as far at any rate as Babylonia, and received the formal submission of the provinces of Iran, while his fleets in the Aegean recovered what his father had lost upon the seaboard, and made fresh conquests as far as Thrace . This moment marks the zenith of the Ptolemaic power . After Ptolemy returned home, indeed, Seleucus regained northern Syria and the eastern provinces, but the naval predominance of Egypt in the Aegean remained, although there are traces of its being replaced locally, towards the end of Euergetes' reign, by that of Macedonia—in Amorgos, Naxos, Syros, Nisyros, Cos and parts of Crete (see Beloch, III . [ii.], p . 463) . After his final peace with Seleucus, Ptolemy no longer engaged actively in war, although his forces might occasionally mingle in the broils of Asia Minor, and he supported the enemies of Macedonia in Greece . It seems probable that his internal policy differed from his father's in patronizing the native religion more liberally; he has left larger traces at any rate among the monuments that are known to-day .