2. The daughter of Ptolemy I. and Berenice, born about B. C. 316, was married in B. C. 300 to Lysimachus, king of Thrace, who was then far advanced in years. Lysimachus had put away Amastris in order to marry Arsinoe, and upon the death of the former in B. C. 288 [AMASTRIS], Arsinoe received from Lysimachus the cities of Heracleia, Amastris, and Dium, as a present. (Plut. Demtr. 31; Paus. 1.10.3; Menmon, apud Phot. p. 225a. 30, ed. Bekker.)
Arsinoe, who was anxious to secure the succession to the throne for her own children, was jealous of her step-son Agathocles, who was married to her half-sister Lysandra, the daughter of Ptolemy I. and Eurydice. Through the intrigues of Arsinoe, Agathocles was eventually put to death in B. C. 284. [AGATHOCLES, p. 65a.] This crime, however, led to the death of Lysimachus; for Lysandra fled with her children to Seleucus in Asia, who was glad of the pretext to march against Lysimachus. In the war which followed, Lysimachus lost his life (B. C. 281) ; and after the death of her husband, Arsinoe first fled to Ephesus, to which Lysimachus had given the name of Arsinoe in honour of her (Steph. Byz. s. v. Ἔφεσος), and from thence (Polyaen. 8.57) to Cassandreia in Macedonia, where she shut herself up with her sons by Lysimachus.
Seleucus had seized Macedonia after the death of Lysimachus, but he was assassinated, after a reign of a few months, by Ptolemy Ceraunus, the half-brother of Arsinoe, who had now obtained the throne of Macedonia. Ptolemy was anxious to obtain possession of Cassandreia and still more of the sons of Lysimachus, who might prove formidable rivals to him. He accordingly made offers of marriage to Arsinoe, and concealed his real object by the most solemn oaths and promises. Arsinoe consented to the union, and admitted him into the town; but he had scarcely obtained possession of the place, before he murdered the two younger sons of Lysimachus in the presence of their mother. Arsinoe herself fled to Samothrace (Justin, 17.2, 24.2, 3; Memnon, apud Phot. p. 226b. 34); from whence she shortly after went to Alexandria in Egypt B. C. 279, and married her own brother Ptolemy II. Philadelphus. (Paus. 1.7. §§ 1, 3; Theocrit. Idyll. 15.128, &c. with the Scholia; Athen. 14.621a.) Though Arsinoe bore Ptolemy no children, she was exceedingly beloved by him; he gave her name to several cities, called a district (νομός) of Egypt Arsinoites after her, and honoured her memory in various ways. (Comp. Paus. l.c. ; Athen. 7.318b. xi. p. 497d. e.) Among other things, he commanded the architect, Dinochares, to erect a temple to Arsinoe in Alexandria, of which the roof was to be arched with loadstones, so that her statue made of