Monte Cassino had been plundered by the Lombards and the monks escaped to Rome to seek protection from Pope Pelagius II.

Subsequently, Catellus was accused of witchcraft by a priest named Tibeius (Tibeio) of Stabia and was held captive at Rome until a new pope released him.

Antoninus became an abbot of the Benedictine monastery of San Agrippino, succeeding Boniface (Bonifacio) in this capacity.

A miracle attributed to Saint Antoninus states that he saved a young child from a whale after it had been swallowed up by this sea creature.

He was credited with saving the city from many dangers: a Moorish naval invasion; the revolt of the Sorrento leader Giovanni Grillo against Spanish domination; demonic possession; bubonic plague; and cholera.