Between late October and early November 220 BC she was married to her brother, Ptolemy IV. She took active part in the government of the country, at least in the measure that it was tolerated by the all-powerful minister Sosibius. She rode at the head of infantry and cavalry to fight Antiochus the Great at the battle of Raphia in 217 BC. She was the mother of Ptolemy V. In summer, 204 BC she was murdered in a palace coup, shortly after the death of her husband. Eratosthenes wrote a manuscript called the Arsinoe, which is lost, the subject being a memoir of the queen. It is quoted by many ancient scholars.