Gradoli, built over a tuff hill, is located nearby Lake Bolsena.
Some news about Gradoli date back to 1113 P.C. when Matilde di Canossa gave the Church a number of possessions, including the Gradolarum Castrum, which made up what is actually known as the Lake Valley.
The Castle of Gradoli was impressive and fortified, it had a fortress and probably a moat, and, even thaugh now turned into streets and squares, its form is still visible.
In the thirteenth century the Church found itself at odds with Orvieto, which has long yearned possession of these and other surrounding lands. During this century the domain of the area alternated by the Church and by Orvieto. The dispute continued until the two sides found an agreement deciding to hold together the dominion over the Lake Valley.
Tired of having two masters, the inhabitants of Gradoli, along with those of other villages, tried with little success to rebel.
In the first half of the fourteenth century Gradoli suffered a serious looting, at the hands of Louis of Bavaria. During this time a handful of 300 valid countrymen tried to resist the siege and destruction, but had to surrender for hunger.
In the fifteenth century the town was then divided between Pope Eugenius and the Farnese family, which whom in 1505 it passed in perpetual vicarage. In this period Gradoli flourished and became a major center of the Duchy of Castro. During the same period Pope Paul III took Gradoli as his residence and demolished the ruins of the old castle building his new residence, the Palazzo Farnese.
After the decline of the family Farnese and the destruction of the Duchy of Castro, Gradoli returned in possession of the Church and in 1871 it definitively joined the Kingdom of Italy.