In the 5th century, Giovanni and Lazzaro, two Syrian hermits who, in search of a secluded place had scaled the Solenne mountain and descended into the Suppenga valley , were said to have founded the Eremitage, already a pagan nucleus, which later on became the Abbey of San Pietro in Valle. Duke Faroaldo II of Spoleto and lord of the lands where the eremitage was situated, constructed the church dedicated to St. Peter with its monastery, which adopted the rule of St. Benedict. Here, Faroaldo himself donned the monk's habit and died in 728. Afterwards, a period of peace and relative popolarity followed, which continued for more than a century.
In the year 840, the monks were deprived of their lands by ths bishop of Spoleto. The abbey, which, afterwards, had been partly destroyed under the first Ottos, was re-erected from the end of the 10thcentury until the 11th centuriy under Otto III and Henry II. From June of 1190 onwards, the abbey of St. Peter in the Valley became the property of the town of Spoleto.
At the end of the 12th century, very probably at the time of Gregory II (1198-1226), it was added to the basilica of St. Giovanni in Laterano; other works of restauration to the buildings and the frescoes in the nave presumably date back to this period. Because of the decay of the monical life, in 1477, Sixtus IV, removed the monks from this monastery and ceded the abbey to the Ancajani family, of who, in various instances, members were accomodating abbots of the abbey, until 1850, when, with the unification of Italy, it became its owner.
The last heir of the Ancajani family ceded the church to the parochy and sold the convento, which will become a historical residence (guest-house). The abbey church was completed in two different periods: during the Longobard (8th century) and the Romanic periods (12th century), but the two styles are inserted in such harmony that one does not notice the progression. Inside the church various Longobard fragments and Roman sarcofagi are to be found; above all, however, also a cycle of pictures, which is very important because of its extensive series of themes from the New and Old Testament, which are to be found and the walls of the church, and make those seem like a picture gallery. The Cloister and the monk's quarters date back to a later period compared to the church, probably near the 12th and 13th centuries.
The northern part of the cloister, which adjoins the nave of the church, is scanned by three high and large arches supportanted by quadrangular pillars. The other three sides show a different situatione: the lower part is made up of porticos with cross-beam vaults supported by mighty and low columms constructed of local stone. The Bell Tower: of a square design, slightly asymmetrical, it represents a a decorated wall made up of a irregular blocks of local stone. Its wall are decorated here and there with "inserts" of preceding epochs; among others, one notes charming fragments of the Roman and Longobard times.