Cetteus was a 6th-century bishop of Amiternum who lived during the pontificate of Pope Gregory the Great. According to tradition, he was elected to his see in 590 during a period of Lombard occupation. He is remembered for his refusal to support the occupying forces, which led to his flight to Rome. After returning to his city following an intervention by the Pope, he was ultimately executed by the Lombard leader Umbolus for his perceived political allegiances.