In 1287, Tommaso, the Bishop of Terni, called his brethren Augustinian monks to take an interest in the church of San Pietro in Tirio and the connected oratory of San Salvatore. If the official founding date of the church today is set at 1287, it is certain that the original nucleus already existed regardless of whether or not it is true, as some people say, peace between the Lombard King Liutprando and Pope Zaccaria was signed in the San Salvatore oratory of the Parish of San Pietro in 741
The Augustinian monks were authorized to build a new church and it is precisely that which still stands today, albeit of the building erected in the 13th century only a part of the bell tower, the apse and the left wing remain.These were transfered to San Pietro from the convent they occupied at Rocca San Zenone, a short way from the consular Flaminia along the stretch that goes from Terni to Spoleto.
The church has undergone several extensions and restoration works starting from 1315 when the adjoining convent was built. Today it is used as a school, but once upon a time it had a certain importance, if only for the fact that it accommodated the Pope twice: in 1450 Pope Nicolò V stopped over for a night with all the members of his court, and in 1646 Pio ll. A later extension was financed in the 15th century by Stefano Manassei, a Terni nobleman who was mayor of Florence, who had his residence nearby. His action ensured his burial inside the church: the tombstone, on which he is sculptured on his deathbed, was originally set in the floor. Following the changes the construction has undergone, it was removed and is now walled on the left wing of the church (therefore in a vertical position) next to the presbytery.
Damaged in 1703 by an earthquake and then by the bombings in World War 11, San Pietro has undergone a series of consolidation interventions and reconstruction work. The damage to the walls had at least the advantage of bringing to light precious frescos dating back to the 14th century among which shines the painting by the anonymous Umbrian artist, who, due to its subject is now known as "Maestro della Dormitio Virginis". But other frescos, often painted by unknown Umbrian artists, are worthy of notice although in some cases they are severely damaged: from the Incoronazione della Vergine, to a Madonna con Bambino.