He built a new Jewish temple at Leontopolis in Ptolemaic Egypt where he reigned as a rival High Priest to the hierarchy in Jerusalem.
[1] Onias III fled to the Seleucid capital Antioch, perhaps hoping to petition King Antiochus IV to restore him, where he was killed by his enemies while attempting to claim sanctuary at the shrine to Apollo and Artemis.
[citation needed] Around 167–166 BCE, the Maccabean Revolt began, with one of its major causes being discontent with the policies of High Priest Menelaus.
Onias IV left Judea for Ptolemaic Egypt at some unknown point, most likely around the time of Alcimus's appointment as High Priest.
[2] Josephus presents two contradicting traditions: in The Jewish War, it is Onias III that flees to Egypt (possibly taking his son with him?).
In Jewish Antiquities, Onias IV leaves for Egypt during the reign of Antiochus V Eupator, around the time of Alcimus's ascension.
The exact date is unknown, but with the permission of Ptolemy VI Philometor, Onias IV arranged the construction of a temple at Leontopolis.
A large number of able-bodied Judeans had accompanied Onias to Egypt, and these strangers, who were there called Κάτοικοι ("inhabitants"), received, on condition of performing military service and preserving the internal peace of the country, tracts of land of their own, on which they lived with their families[6] The district inhabited by them lay between Memphis and Pelusium, and was long called the "land of Onias.