Now to attempt to date the design, we must remember that the palazzo Cornaro was bought on October 18, 1647, and the Gomez family was not removed until November of the following year. This still left the palazzo to the right, which was more difficult to acquire, and the first warning was sent to the Abbots in 1648 invoking the Gregorian Constitution. This signifies that a plan had to be in existence at that time, and would have to be included with any legal documents dealing with this case. Then, it is important to remember that through Lady Olimpia, Bernini, by some means, was able to depose Borromini, regain favor with Innocent X in late 1647, and obtain the commission for the Four Rovers Fountain It then makes sense that the Bernini lost original for the reorganization of the three palazzo of Lady Olimpia, should be dated to late 1647.
It may be said that if Bernini carried this design out for the Trevi Fountain, complete with rocks and Mount Parnassus, it would be in poor condition because there was such little water. Several factors are involved when addressing this fact. Water was an issue. Bernini was already aware of this as he was working on the Four Rivers Fountain, ordered by the Pope, to be located in front of the Pope’s family residence in Piazza Navona. The Pope had also decreed that 150-180 ounces of water needed to be diverted from the water of the Trevi. In the mind of the Pope, this solved the problem. This would cause the Trevi Fountain to lose its importance, causing Alexander VII to consider moving the fountain to the Piazza Colonna. In the 1647 design by Bernini, the fountain had much less water and could not be as enormous as Bernini envisioned. 100 years later, in 1744, Salvi increased the water supply by lining in more springs. Therefore, in the meantime, to make up for the lack of water, the fountain had to become more decorative, since it was lacking in importance. This was also a result of the need to unite the façade, since Lady Olimpia had acquired all three of the buildings.
In conclusion to this long section, it is important to consider one valuable fact, and that is the notorious rivalry between Borromini and Bernini, revealed rather frequently in their work. If Gian Lorenzo was the one to set about creating the facade, the enormous and very striking pool of his fountain would totally fill the area between Palazzo Pamphili and Palazzo Carpegna opposite (which is now the Accademia di San Luca). This would involve the demolishing of the whole, or at least most, of the latter, which was, at the same time, being built by Borromini.