He was a bishop of the 6th century, elected to the see of Amiternum in Sabina (today the city of San Vittorino) in 590, during the pontificate of Gregory the Great.

[1] According to a largely legendary[1] Passio, during Cetteus’ episcopate, Amiternum was occupied by two Lombard captains, Alai and Umbolus.

Pope Gregory convinced Cetteus to return, however, after receiving a promise from the Lombards that they would treat the city's inhabitants with humanity.

The saint's name was eventually discovered, and the body was buried in the church in Pescara that was later dedicated to him, San Cetteo.

Although largely legendary, the Passio is probably correct in placing Cetteus' death at the time of the Lombard invasion.