The Cathedral is the result of a series of constructions and interventions that have taken place over the centuries. Local tradition says that the first Cathedral, which now corresponds to the Crypt, it has been built on the ruins of a pagan temple of the Holy Bishop Anastasius, in the sixth century. From Romanesque Cathedral are little remains. The facade has a large porch with a double row of columns, in which there are three doors of the Romanesque style, adorned with friezes. The top of the facade is a modern work by Marcello Piacentini, consists of a travertine balustrade and statues of eight bishops of Terni, including St. Valentine. The interior has a Latin cross with three naves separated by pillars, with side chapels, transept and apse. In the crypt, there is the tomb of Saint Anastasius, built using a pagan altar.