Pope St. Pius I

Pope St. Pius I governed the Roman Church in the middle of the second century, reigning by tradition from about 142 to 155. An ancient source, the Muratorian Fragment, records that he was the brother of Hermas, author of the early Christian work The Shepherd, a widely read book of visions and moral exhortation, which places Pius among the notable figures of the Roman Church of his day.

His pontificate was marked by the continuing struggle against Gnostic error, for it was during his reign that the heretics Valentinus and Marcion were active and were resisted at Rome. He is also associated by tradition with fixing the manner of calculating the date of Easter. Venerated as a saint and by tradition a martyr, though the historical evidence for his martyrdom is uncertain, he is remembered as a defender of the faith against heresy, and is celebrated on 11 July.