Passage 1.7.2
καὶ Πτολεμαῖος μὲν τὴν ἐσβολὴν φραξάμενος ὑπέμενεν ἐπιόντας Κυρηναίους, Μάγᾳ δὲ ἀπαγγέλλεται καθʼ ὁδὸν ἀφεστηκέναι Μαρμαρίδας· εἰσὶ δὲ Λιβύων οἱ Μαρμαρίδαι τῶν νομάδων. καὶ τότε μὲν ἐς Κυρήνην ἀπηλλάσσετο· Πτολεμαῖον δὲ ὡρμημένον διώκειν αἰτία τοιάδε ἐπέσχεν. ἡνίκα παρεσκευάζετο ἐπιόντα ἀμύνεσθαι Μάγαν, ξένους ἐπηγάγετο καὶ ἄλλους καὶ Γαλάτας ἐς τετρακισχιλίους· τούτους λαβὼν ἐπιβουλεύοντας κατασχεῖν Αἴγυπτον, ἀνήγαγε σφᾶς ἐς νῆσον ἔρημον διὰ τοῦ ποταμοῦ. καὶ οἱ μὲν ἐνταῦθα ἀπώλοντο ὑπό τε ἀλλήλων καὶ τοῦ λιμοῦ·
Ptolemy, having secured the entrance, awaited the approaching Cyrenaeans. But a report came to Magas along the way that the Marmaridae had revolted. These Marmaridae are nomadic Libyans. Thus at that time he withdrew to Cyrene. But when Ptolemy was ready to pursue him, he was prevented by the following circumstance. When constructing his defenses against the advance of Magas, he had brought in foreign mercenaries, including some four thousand Galatians. Learning that these intended to seize control of Egypt, he conveyed them to a deserted island by way of the river. There they perished, partly at each other's hands and partly through famine.