In the summer of 357, Ursacius and Valens, the advocates of this latter group of dissidents in the West, through the influence which they were enabled to bring to bear upon the Emperor by means of his second wife, Aurelia Eusebia (Panegyr. Jul. Orat., iii; Ammianus, XXI, vi, 4), succeeded in bringing about a conference of bishops at Sirmium.
He was the leader of a council at Sirmium in 351, held against Photinus who had been a deacon at Ancyra, and the canons of this synod begin by condemning Arianism, though they do not quite come up to the Nicene standard.
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Basil persuaded Constantius to summon a general council, Ancyra being proposed, then Nicomedia (both in Asia Minor), but as the latter city was destroyed by an earthquake, Basil was again at Sirmium in 359 where the Arianizers had meanwhile regained their footing; with Germinius of Sirmium, George of Alexandria, Ursacius and Valens, and bishop (later saint) Marcus of Arethusa, he held a conference which lasted until night.
The Triballian King Syrmus was later considered the eponymous founder of Sirmium, but the roots are different, and the two words only became conflated later.
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Aurelius Victor, prefect of the Pannonia Secunda province (369), and author of a History of Rome until the reign of Julian.
Thurisind seems to have given to his eldest son the rank of commander of the Gepids in the city of Sirmium as a way to guarantee his succession to the throne, as this position made him heir apparent.
In late summer 351 he was in Sirmium, member of the tribunal processing Photinus; the city was under control of the area under control of Emperor Constantius II, while Rome was occupied by usurper Magnentius.
Saint Serenus the Gardener (Sirenatus, Cerneuf), also known as Serenus of Sirmium
It became one of the primary settlements of Moesia, situated between Sirmium (modern Sremska Mitrovica) and Viminacium (modern Kostolac), both of which overshadowed Singidunum in significance, and just across the Sava River from Taurunum (modern Zemun) in Pannonia.