Arsinoe II (Greek: Αρσινόη) (316 BC-July 270 BC), queen of Thrace and Macedonia and later co-ruler of Egypt with her brother and husband Ptolemy II of Egypt. She was the daughter of king Ptolemy I Soter (Greek : Πτολεμαίος Σωτήρ, which means savior), the founder of the Hellenistic state of Egypt, and his second wife Berenice I.
Arsinoe II was, at the age of 15, married to King Lysimachus of Thrace, (Greek : Λυσίμαχος) to whom she bore three sons, Ptolemy, Lysimachus and Philip. In order to position her sons for the throne, she had Lysimachus's first son, Agathocles, poisoned on account of treason. After Lysimachus' death in battle in 281 BC, she fled to Cassandrea (Greek : Κασσάνδρεια), Greece and married her half-brother Ptolemy Keraunos, son of Ptolemy I from his first wife, Euridice. The marriage was for political reasons as they both claimed the throne of Macedonia / Thrace (by the time of his death Lysimachus was ruler of both regions, and his power extended to south Greece as well). Their relationship was never good. As Ptolemy Keraunos was becoming more powerful, she decided it was time to stop him and conspired against him with her sons. This action caused Ptolemy Keraunus to kill two of her sons, Lysimachus and Philip, while the elder, Ptolemy, was able to escape and to flee north, to the kingdom of the Dardanians. She herself went to Alexandria, Egypt to seek protection from her brother, Ptolemy II.
In Egypt, she continued her intrigues and probably instigated the accusation and exile of her brother Ptolemy II's first wife, Arsinoe I of Egypt. Arsinoe II then married her brother; as a result, both were given the epithet "Philadelphoi" ("Brother-Loving") by the presumably scandalized Greeks. Arsinoe II shared all of her brother's titles and apparently was quite influential, having towns dedicated to her, her own cult (as was Egyptian custom), and appearing on coinage. Apparently, she contributed greatly to foreign policy, including Ptolemy's victory in the First Syrian War (274-271 BC) between Egypt and the Seleucid Empire in the Middle East. After her death, Ptolemy II continued to refer to her on official documents, as well as supporting her coinage and cult. He also established her worship as a Goddess, a clever move, because by doing this he established also his own worship as a God.