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).