the account. The heretics Valentinus, Cerdon, and Marcion visited Rome during that period. Catholic apologists see this as an argument for the primacy of the Roman See during the 2nd century. Pope Pius I is believed to have opposed the Valentinians and Gnostics under Marcion, whom he excommunicated. There is some conjecture that Pius was a martyr in Rome, a conjecture that entered earlier editions of the Roman Breviary. The study that had produced the 1969 revision of the General Roman Calendar stated that there were no grounds for his consideration as a martyr, and he is not presented as such in the Roman Martyrology. Feast day Pius I's feast day is 11 July. In the Tridentine Calendar it was given the rank of "Simple" and celebrated as the feast of a martyr. The rank of the feast was reduced to a Commemoration in the 1955 General Roman Calendar of Pope Pius XII and the General Roman Calendar of 1960. Though no longer mentioned in the General Roman Calendar, Saint Pius I may now, according to the rules in the present-day Roman Missal, be celebrated everywhere on his feast day as a Memorial, unless in some locality an obligatory celebration is assigned to that day. See also List of Catholic saints List of popes References 1st-century births 154 deaths 2nd-century archbishops 2nd-century Christian martyrs 2nd-century Romans Christian slaves and freedmen Italian popes Papal saints People from Aquileia Popes Year of birth unknown 2nd-century popes Imperial Roman slaves and freedmen Burials at St. Peter's Basilica Christian anti-Gnosticism