The very first news about Bagnaia dates back to 963, when it is referred to as a village called Bangaria. A document from the imperial delegate Christian, Archbishop of Mainz, confirms Bagnaia as a possession of Viterbo.
In 1201, the land was donated to Guido and John Pennant, who in turn sold it to St. Mary of Palanzana, in order to remove Bagnaia from Viterbo.
This attempt to dismiss Viterbo, however, failed miserably, so that in 1202 a bull of Pope Innocent III, confirmed the possession of Bagnaia by Viterbo.
During the thirteenth century Bagnaia was donated by the Pope to the Bishop of nearby Viterbo, even though until the sixteenth century was not built there any Bishop's residence.
The Middle Ages but especially the Renaissance, were characterized by the construction of several architectural works that have reached their zenith with the splendid Villa Lante.
Questo tentativo di allontanare Viterbo, però, fallì miseramente, tanto che nel 1202 una bolla di Innocenzo III, confermò il possesso di Bagnaia da parte di Viterbo.
Nel XIII secolo, venne donata dal Papa al Vescovo della vicina Viterbo, anche se fino al XVI secolo non vi fu costruita alcuna residenza vescovile.
The villa, commissioned by Cardinal Gianfrancesco Gambara in 1566, is one of the buttonhole flowers of Tuscia, with its Italianstyled garden, the many fountains and water features.
In 1576 a Sienese architect, Thomas Ghinucci, performed a reorganization of the village from the urban point of view, that led Bagnaia to become a small town.
The most visible aspects of this new urban study can be found in Piazza XX Settembre, it realized taking as inspiration the Piazza del Popolo in Rome.