Pontificate: Sept. 24, 366 to 367. Ursinus was a Roman deacon and a supporter of Pope liberius (352–366) in his struggles against the emperor constantius ii (337–351) and the antipope felix (355–365). When Liberius died, his supporters elected Ursinus as his sucessor, and they took up a position in the Julian basilica. However, adherents of Felix and some other Roman clergy and lay people elected damasus i (366–384) pope. The rivals' partisans engaged in bloody street battles, usually won by Damasus' men. When Damasus had sufficient strength, he got the city prefect to exile Ursinus and his chief followers. Ursinus successfully petitioned the emperor Valentinian I (364–375) for permission to return to Rome. He and his supporters triumphantly entered the city on Sept. 13, 367, but trouble broke out again, and regretting his earlier decision, Valentinian exiled Ursinus to Gaul. When his followers promised the government that they would maintain the peace with Damasus, the emperor released Ursinus from exile. He moved to northern Italy and immediately began plotting against Damasus. In 370 the Ursinians in Rome got a converted Jew named Isaac to accuse him of a "disgraceful" crime, apparently adultery. For a time Damasus found himself in a precarious position, but he soon extricated himself. The emperor decided that Ursinus simply could not be allowed to stay in Italy and so exiled him to Cologne. No one is sure what happened to him there, but some northern Italian bishops spoke of his machinations as late as 381. When Damasus died in 384, Ursinus let the Romans know of his availability for the papal office, but they chose Siricius (384–399). After that Ursinus disappeared from history.
[j. f. kelly]