The origins of Trevi are lost in time. It was classified as an Umbrian town by Latin authors, but paleolithic ruins in the area testify an earlier prehistoric civilisation. Its importance grew in particular under Roman rule when the old Flaminia Way was restored; it developed in the valley where, in the locality of Pietrarossa, remains and ruins of the original "civitas" with its monumental buildings are to be found. On the hilltop the original fortified town developed with its massive and robust 1^st century walls, parts of which are still intact and visible today.

In ancient times its territories covered vast areas of the surrounding hills and valleys, with. fertile land around the river Clitunno and communications secured by the Flaminia; it was also a diocese till the end of the 11^th C.

Under the Longobards it was a Stewardship and then eventually a free commune (beginning 13thC). Allied with Perugia against Spoleto, it only became autonomous in 1389 after various fights with neighbouring communes. Subsequent dominions followed, the most disastrous being the Trinci’s of Foligno till 1438. It returned under Perugia and Church control and then followed the fortunes of the Papal States till the Unification of Italy.

Trevi was most prosperous in the early Middle Ages and during the Renaissance Period. Trade boomed (it was called the "dry Port" and the arts expanded. In 1469 one of the very first Monti di Pietà (pawnshops) was opened and in 1470 a printing press was set up by the earliest press association on record. (The press was the fourth in the whole of Italy )