Bolsena is a small town in Central Italy, situated on the shores of the lake of the same name. The peculiarity of Bolsena is that there are three towns, at three different levels: the Roman one on top, of which only the ruins are extant, the Medieval one in the middle, and the Renaissance one at the bottom. The film illustrates the historical events accounting for this particular urban complex. We gradually come to understand the role played by the Cassian Road in the history of Bolsena and the way in which this has affected the relation between the town and its territory through the centuries. The film does not follow a particular chronological order. This apparently random order actually gives the documentary its lively pace. In addition, computer reconstructions facilitate the understanding of historical events. These illustrate places and buildings dealt with in the film, wich are no longer visible nowadays, by means of effective symbols and colours.