On the basis of archival documents, the author reviews the building and planning history of Villa Mattei or Villa Celimontana on the Caelius hill of Rome: the original layout designed by Giacomo Del Duca; the construction of the obelisk, the water distribution system, fountains, sculptures, etc., designed by G. and D. Fontana, commissioned by Ciriaco Mattei and his son Giovanni Battista; later extensions and completions.