Encyclopaedia Britannica, 11th Edition, "Armour Plates" to "Arundel, Earls of"

1. Daughter of Lysimachus, king of Thrace, first wife of Ptolemy II.

Philadelphus (285-247 B.C.). Accused of conspiring against her husband, who perhaps already contemplated marriage with his sister, also named Arsinoe, she was banished to Coptos, in Upper Egypt. Her son Ptolemy was afterwards king under the title of Euergetes. It is supposed by some (e.g. Niebuhr, _Kleine Schriften_; cf. Ehrlichs, _De Callimachi hymnis_) that she is to be identified with the Arsinoe who became wife of Magas, king of Cyrene, and that she married him after her exile to Coptos. But this hypothesis is apparently without foundation. Magas before his death had betrothed his daughter Berenice to the son of his brother Ptolemy II. Philadelphus, but Arsinoe, disliking the projected alliance, induced Demetrius the Fair, son of Demetrius Poliorcetes, to accept the throne of Cyrene as husband of Berenice. She herself, however, fell in love with the young prince, and Berenice in revenge formed a conspiracy, and, having slain Demetrius, married Ptolemy's son (see BERENICE, 3).