HE was a priest among the Roman clergy in 418, when Pope Zozimus condemned the Pelagian heretics. Sixtus was the first, after this sentence, who pronounced publicly anathema against them, to stop their slander in Africa that he favoured their doctrine, as we are assured by St. Austin and St. Prosper in his chronicle. The former sent him two congratulatory letters the same year, in which he applauds this testimony of his zeal, and in the first of these letters professes a high esteem of a treatise written by him in defence of the grace of God against its enemies. It was that calumny of the Pelagian heretics that led Garnier into the mistake, that our saint at first favoured their errors. But a change of this kind would not have been buried in silence. After the death of St. Celestine, Sixtus was chosen pope, in 432. He wrote to Nestorius to endeavour to reclaim him after his condemnation at Ephesus, in 431: but his heart was hardened, and he stopped his ears against all wholesome admonitions. The pope had the comfort to see a happy reconciliation made, by his endeavours, between the Orientals and St. Cyril: in which he much commended the humility and pacific dispositions of the latter. He says, “that he was charged with the care and solicitude of all the churches in the world, 1 and that it is unlawful for any one to abandon the faith of the Apostolic Roman Church, in which St. Peter teaches in his successors what he received from Christ.” 2 When Bassus, a nobleman of Rome, had been condemned by the emperor, and excommunicated by a synod of bishops for raising a grievous slander against the good pope, the meek servant of Christ visited and assisted him in person, administered him the viaticum in his last sickness, and buried him with his own hands. Julian of Eclanum or Eeulanum, the famous Pelagian, earnestly desiring to recover his see, made great efforts to be admitted to the communion of the Church, pretending that he had become a convert, and used several artifices to convince our saint that he really was so: but he was too well acquainted with them to be imposed on. This holy pope died soon after, on the 28th of March, in 440, having sat in the see near eight years. See his letters, Anastasius’s Pontifical, with the notes of Bianchini, &c.
Butler’s Lives of the Saints