Saint Peter: an angel releases him from prison. Colour lithograph by C. Mariannecci, 1862, after Filippino Lippi.

Bible, N.T. Acts 12.6-9. On the right, the armed prison guard sleeps. A fisherman on the lake of Genezareth in Galilee, Saint Peter was, with his brother Andrew, the first of the Apostles. His name was Simon; he was renamed Peter (Kephas in Aramaic, Petros in Greek) by Jesus to indicate that he would be the cornerstone (petra) of the Church. Often depicted with one or two keys, representing his role as gatekeeper of heaven. In the Middle Ages he was invoked against fevers, bouts of madness and snake-bite. Because Peter had put to flight the dogs sent against him by Simon the Magus (in the apocryphal Acts of Peter), hot keys called "the key of St. Peter" (clef de Saint Pierre) were applied to dogs and ther owners to protect them from rabies