The abbey was mentioned for the first time in documents of the Carolingian period, in 762 on a preceeding Roman installation of the fifth century attributed to a certain Gallae, told by a monk of the community of San Silvestro on nearby Mount Soratte. History has it then that this abbey was sought by a brother of 'Pepin the Short', who retired in contemplation in this area, and it was built by Benedictine monks. After 1000, the Abbey remained among the possessions of the monastery of St. Paul Outside the Walls in Rome, and then passed under the administration of the Farnese. The Romanesque style dates back to the twelfth century and was originally a fortified church with control towers like all centres located in a strategic location along the trade routes. The only surviving tower is the bell tower. The interior has three naves with granite columns and Ionic and Corinthian capitals, and the floor is covered with cosmatesque (cosmati) mosaics.