Tolfa is a town and comune of the province of Rome, in the Lazio region of central Italy; it lies to the ENE of Civitavecchia by road.

It is the main center in the Monti della Tolfa, an extinct volcanic group between Civitavecchia and the Lake of Bracciano.

A beautiful town of medieval origin in the orbit of Viterbo, it was assumed into the Papal States and granted first to the Capocci family, and then to the Roman nobles Ludovico and Pietro Frangipani who walled the community. Tolfa achieved sudden importance following the discovery there in 1461 of large deposits of alunite, the source of alum, with the result that direct control was assumed, after some confrontations with the Frangipani, by the Camera Apostolica. Alum was an essential mordant in the textile industry, which was central to the Late Medieval and Early Modern Italian economy. Previously, the only supplies of alum were imported from the East, from sources controlled by the Ottoman Turks, through Venice, which profited greatly. Suddenly, the monopoly of alum shifted to the Papacy, which controlled Tolfa; Pope Pius II placed its distribution solely in the hands of the Medici, with the explicit thought that the income from this monopoly should be devoted to the Christian res publica as the infidel Turk, elated by his victories, threatened to devour Christendom. Later the monopoly in extraction of alum at Tolfa passed as a papal gift to Agostino Chigi.