According to Catholic tradition, Pius I governed the Church in the middle of the 2nd century during the reigns of the Emperors Antoninus Pius and Marcus Aurelius. He is held to be the ninth successor of Saint Peter, who decreed that Easter should only be kept on a Sunday. Although credited with ordering the publication of the "Liber Pontificalis", compilation of that document was not started before the beginning of the 6th century. He is also said to have built one of the oldest churches in Rome, Santa Pudenziana.