This fountain is not the first one to be erected on Monte Cavallo, but the first fountain was as subservient as the present one to the colossal groups which have given the name “Cavallo” to this entire district. The Dioscuri were once a part of a kind of open-air museum which, during the earliest days of the papacy, existed on the slope of the Quirinal Hill. Gregory XIII had them removed to the Capitol, but when Sixtus V had purchased from the heirs of Cardinal Caraffa the site and the partly erected buildings of the Quirinal, he brought them back again and subjected them to a thorough restoration, using for this purpose the material from the base of one of them. There has existed a villa on this spot antedating Pope Sixtus V’s time by many years. It had been called the Villa d’Este, but it should not be confused with the Villa d’Este, at Tivoli, although it was built by the same Cardinal Ippolito of that family. Sixtus V was extremely fond of this portion of the city and with Fontana’s assistance he created the magnificent palace and surroundings which ever since his day have been associated with sovereign power in Rome. Fontana enlarged the piazza before the palace in order to make it “commodious for consistories,” and he also lowered the grade in order to bring hither the Acqua Felice. There must have been many discussions between Pope Sixtus V and his architect with regard to the fountain on the Quirinal. Everything that Sixtus V did he did thoroughly and magnificently, and it was quite natural that he should desire a splendid fountain before his own palace, considering that it was he himself who had made it possible, by the introduction of the Acqua Felice, to have a fountain in that place at all. A rare old engraving shows that the fountain, as at first planned, resembled the Fountain of the Moses. In it the Dioscuri occupy the niches as does the Moses in the fountain on the Viminal. This plan was happily abandoned. The great classic figures were erected as they stand to-day in front of the palace, and Fontana placed between the two groups, in the same position as the fountain of the present day, the conventional large basin and central vase which is to be seen in the old engravings of the seventeenth century. It was certainly neither a very original nor a very interesting design and it must have relied for its effect entirely upon the copious supply of water which was described by Evelyn in 1644 as “two great rivers.”