St. Pius I, according to the "Liber Pontificalis," was an Italian from Aquileia. His father's name was Rufinus. He was a brother of the famous Hermas, the author of "The Shepherd," a precious early Christian document. Hermas in this work says that he was a slave and then a freedman. This, however, is quite possibly a fictional device of the author. If it is true, it would indicate that St. Pius was of a low social origin.

St. Pius had to cope with the Gnostic heretics who were active at Rome during his reign. The Pope excommunicated a Gnostic leader named Marcion, who thereupon set up his own church. But if heretics afflicted the soul of St. Pius, he must have been consoled by the visit of St. Justin, the great defender of Christianity. Justin was a convert from paganism. He had a restless desire for truth which had led him through the Stoic, Platonic, and Pythagorean schools of philosophy to the Bible and Christianity. Not content with securing peace of soul through Christ, Justin wrote much to defend Christ's doctrines, and finally died a martyr.

According to the "Liber Pontificalis," Pope St. Pius ordered that a heretic coming from the Jews should be received and baptized. This is somewhat obscure, and it is not certain whether he meant a heretic in the modern sense, i.e., some Judaeo Christian, or a real Jew.

Later legend credits St. Pius with establishing the two Roman churches of St. Pudens and St. Praxedes, but this lacks historical justification.

St. Pius is honored as a martyr by the Church. He was buried near St. Peter on the Vatican. His feast is kept on July 11.