His pontificate was marked by the efforts of various heretics in Rome, among them the gnostics Valentinian, Cerdon, and Marcion, to sow their errors in the Church’s center. The last-named, when excluded from communion by Saint Pius, founded the heretical group which bears his name. Saint Justin and other Catholic teachers assisted the Pontiff in defending Christian doctrine and preserving it from corruption. After having governed the Church for fifteen years Saint Pius I obtained the crown of martyrdom by the sword, in the year of Our Lord 150.
Saint Pius I, born in the State of Venice, succeeded Saint Hygin in the year 142 as the ninth successor to Saint Peter, during the reign of the emperor Antoninus the Pious. Throughout his pontificate he took great care to make the religion of Christ flourish, and published many beautiful ordinances for the utility of the universal Church. In his decrees he was severe towards blasphemers and with the clergy who showed negligence for the divine Mysteries of the altar. Saint Pius ordained that Easter be celebrated on a Sunday; in this way the custom which the Apostles had already observed became an inviolable law of the Church.