Terni is the ancient Interamna Nahars of the Umbrians, and the cathedral, and other churches, are built on the sites of pagan temples. After the Lombard invasion, Terni belonged to the Duchy of Spoleto, and with the latter, came into the Pontifical States; it was at Terni that Pope Zacharias entered into the agreement with King Luitprand for the restitution of the cities of Bieda, Orte, Bomarzo, and Amelia to the Duchy of Rome.
It is believed that the gospel was preached at Terni by St. Peregrinus, about the middle of the second century. St. Valentinus has a basilica outside the city. There were other martyrs from this city among them, Sts. Proculus, Ephebus, Apollonius, and the holy virgin Agape.
In the time of Totila, the Bishop of Terni, St. Proculus, was killed at Bologna, and St. Domnina and ten nuns, her companions, were put to death at Terni itself. After the eighth century Terni was without a bishop until 1217, in which year the diocese was re-established.
Among its bishops were: