It was to be decorated with the figure of the god of seas (Marforio), lying in a grotto, which was at that time excavated at Forum Romanum and which today is found on one of the courtyards of the Capitoline Museums (Musei Capitolini). The figure was to be in tune with the Column of Marcus Aurelius found in the center of the square thus creating a uniform, concise composition. Nothing came out of della Porta’s plans and in the end it was decided to build a rather modest octagonal fountain with rounded sides, decorated only with ribbons of white marble, at the end of which there are two small lion heads. In the middle a mechanism was placed, that allowed the water to cascade down into the basin surrounded with four pyramids spouting water. The fountain itself was placed on a pedestal with five steps. Its second name (Fontana di Portasanta) is derived from the material of which the basin was made – very valuable Greek marble from the Island of Chios with a pinkish color.

The discarded sculpture concept was recalled one hundered years later – much was planned but in the end nothing was done. The appearance of the fountain was changed during its modernization in 1830, when it acquired its present-day form. The pyramids spouting water were removed, while the central decorative part was exchanged for a rather small, brown vasque, from which the water flows into the lower basin. In the bowl itself, sculptures of dolphins with intertwining tails covered with shells were placed on the shorter sides.