PIO I, POPE, saint. – In the Roman Martyrology he is commemorated on 11 July; it was Ado who first inserted him in his Martyrology. He succeeded Hyginus, but the chronology, approximately 140–155, is uncertain. At his death he is said to have been buried near the tomb of St Peter.
From the so-called Muratorian Fragment it is known that Hermas (v.), the author of the Shepherd. During his pontificate the Gnostics Valentinus and Cerdon spread their doctrines in Rome, but the latter returned to Catholic communion for a certain period.
Late and legendary hagiographical traditions, also taken up by the author of the Lib. Pont., make him a native of Aquileia and associate him with the title of Pudens (v.).
BIBL.: Eusebius, Hist. col., IV, 11; Lib. Pont., I, p. 132 ff.; Acta SS. Julii, III, Paris 1868, pp. 170–72; Martyr. Romanum, p. 281 ff. Agostino Amore