According to legend, Gallese was founded by Haleso, son of Agamemnon, who in doing so began the lineage of Falisci. The city was built on a tufa plateau near two rivers.
In the third century BC the area was taken by the Romans who moved to the valley centre where there were important trade routes such as the Via Flaminia, Via Amerina and the port on the Tiber.
The current village was formed in the Middle Ages, when because of the invasions, the inhabitants took refuge in a castle protected by walls on the same plateau where the Falisci had settled centuries before.
In 733 the town was sold by the Duke of Spoleto, Trasimondo, to Gregory III who made a bishopric and built several churches. The cathedral square and the town is probably just above the ancient acropolis of the Falisco centre. The bishops held a liturgical role, political and administrative roles, together with citizens’ representatives.
The town was now very devoted to the Church and from there two popes came: Martin I in 882 and in 892 Romano I.
The prestige it acquired thanks to its religious importance led to several pilgrims coming to Gallese, among them the Cistercian monaco Quardo from Cologne who died in 1150. After his death he was canonized by Adrian IV with the name of San Famiano and today is the patron of the town.
In the eleventh century it was conquered by Gerardo, Count of Sutri and then enjoyed a period of autonomy before being subdued by Viterbo.
In 1576 the ordinances were created that regulated the life of the city based on the Statutes of the thirteenth century. In 1585 the town was elevated to the rank of a duchy by Pope Sixtus V.
Many families have succeeded at the helm of the town, as often happened when a new pope was appointed. Pope Alexander VI Borgia, for example, turned it over to his son Giovanni, Julius II to the Della Rovere, and Paul IV to his nephew Giovanni, Duke of Paliano. It was then the turn of the Altemps and, afterwards, the current owners, the Hardouin, appointed Dukes of Gallese in 1861 by Pius IX.