Saint Sylvester I was the thirty-fourth Pope. He was elected to the Chair of Saint Peter in 314, the year after the Emperor Constantine had ended the bloody persecution of the Catholic Church. Saint Sylvester was the Pope who instituted the first Roman Martyrology. He was very devoted to Church music. He is responsible for the Nicene Creed in the Mass and also put in the Mass the invocation Kyrie Eleison (Lord, have mercy). He was the Pope of the First Ecumenical Council at Nicea in 325, when Arius, a heretic who denied the Divinity of Jesus, was formally condemned.
See also: Soloviev’s Meditation on the Papacy