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In 358, the Roman Emperor Constantius II requested two councils, one of the western bishops at Ariminum and one of the eastern bishops (planned for Nicomedia but actually held at Seleucia Isauria) to resolve the Arian controversy over the nature of the divinity of Jesus Christ, which divided the 4th-century church.
In July 359, the western council (of about 300 or over 400 bishops) met. Ursacius of Singidunum and Valens of Mursa soon proposed a new creed, drafted at the Fourth Council of Sirmium in 359 but not presented there, holding that the Son was similar to the Father "according to the scriptures," and avoiding the controversial terms "same substance" and "similar substance." Others favored the creed of Nicaea.
The opponents of Sirmium wrote a letter to the emperor Constantius, praising Nicaea and condemning any reconsideration of it, before many of them left the council. The supporters of Sirmium then issued the new creed and sent it through Italy.
Pope Liberius of Rome rejected the new creed, prompting Phoebadius of Agen and Servatius of Tongeren to withdraw their support from the homoian. The supporters of Sirmium deposed Liberius and reappointed Felix of Rome in his place.
Those favoring the Creed drafted at Sirmium included:
Those favoring the Creed of Nicaea included: