Pliny the Elder mentioned Trevi as a city of the ancient Umbrians. Under emperor Hadrian the main road through the territory, the Via Flaminia, encouraged the growth of a suburb in the plain at the place now called Pietrarossa, where excavations have brought to light Roman baths that appear to have been still more or less in use in the time of St. Francis, who is known to have visited the area and to have advised people to bathe there.
The seat of a bishop until the 11th century, Trevi was a Lombard viceroyalty (gastaldato), then, in the early 13th century, became a free commune, usually allied with Perugia against nearby Spoleto, and fought several wars with other neighboring communes. In 1438 Trevi passed under the temporal rule of the Church as part of the legation of Perugia, and thenceforth its history merges first with that of the States of the Church, until in 1860 it was united to the Kingdom of Italy.
In 1470, along with Foligno, Trevi became the fourth town in Italy to have a printing press, managed by the first known printing company.