Decreed that in emergency any kind of water could be used for Baptism.
Struggled with bishops of Asia and Africa so Easter should be celebrated according to the Roman rite, not the Jewish one, at one point excommunicating them all. Condemned the heresy of Theodotus the Leather-seller who attracted followers in Rome by preaching that Jesus was a normal man imbued with supernatural powers by Baptism.
SaintJerome refers to him as the first Latin writer in the Church, but only his letters concerning Easter have survived.