If the sketch was what Borromini had in mind for this fountain, it would have been simple for Bernini to outdo him is style and theatricality. Borromini completed the work on the conduits in November of 1647, and the handover of power to Bernini was officially recognized in July of 1648. Innocent gave instruction for the obelisk to be erected in the Piazza, and arranged for the fountain, in accordance to the design created by Bernini. It becomes clear that Bernini was working to great effect, through his works and his contacts. Bernini continued to make alterations to his plan, with the clay model being totally different the final design. There were also two preparatory sketches done for the fountain. The first sketch is the oldest and is located in the Chigi archive. It features the obelisk at the top, and beneath is a bust of an old river deity emerging from a cave in the rocks with its arms raised holding to the right and left, the two crests of Innocent X. Water falls from the cave into a large shell of the four rivers fountain with its sides resting on the rocks, and then into a huge round shallow pool. The second sketch is located in the Windsor Collection. Although somewhat similar, it has little in common with the other sketch. It features four figures, with each sitting on a group of rocks, with water falling into four separate large shells beneath. The shells are supported by four enormous fish that spout water into the air. There is a ring of posts surrounding the pool which is very shallow. Both sketches incorporate the use of the obelisk appears in both these designs, so that means the sketches come from after April 1647, when the Pope had decided to have it rebuilt.
