LIBERIUS, pope from 352 to 366, the successor of Julius I., was consecrated according to the Catalogus Liberianus on May 22. His first recorded act was, after a synod had been held at Rome, to write to Constantius, then in quarters at Arles (35354), asking that a council might be called at Aquileia with reference to the affairs of Athanasius; but his messenger Vincentius of Capua, so far from being successful in his mission, was himself compelled by the emperor at a conciliabulum held in Arles to subscribe against his will a condemnation of the orthodox patriarch of Alexandria. In 355 Liberius was one of the few who, along with Eusebius of Vercelli, Dionysius of Milan, and Lucifer of Cagliari, refused to sign the condemnation of Athanasius, which had anew been imposed at Milan by imperial command upon all the Western bishops; the consequence was his relegation to Berœa in Thrace, Felix II. (antipope) at the same time being consecrated his successor by three “catascopi haud episcopi,” as Athanasius called them. At the end of an exile of more than two years he yielded so far as to subscribe the third Sirmian formula giving up the “homoousion,”—an act which procured his immediate and triumphant return to Rome, but has ever since caused considerable embarrassment to maintainers of the indefectibility of Roman orthodoxy. The remainder of his pontificate was uneventful. He died on September 24, 366, and was succeeded by Damasus I. With the rest of the first sixty popes he shares the title of “Saint.” His biographers used to be perplexed by a letter purporting to be from Liberius, in the works of Hilary, in which he seems to write, in 352, that he had excommunicated Athanasius at the instance of the Oriental bishops; but the document is now held to be spurious. See Hefele, Conciliengesch., i. p. 648 sq.