On the opposite sides of the obelisk in St. Peter's square there are two fountains. The fountain on the left, when facing St. Peter’s Basilica, was designed by Carlo Moderno. In 1612 Pope Paul the V rebuilt the ancient Roman aqueduct the Aqua and it was renamed the Acqua Paola. The restored aqueduct provided the fountain with a larger source of water. The architect Carlo Maderno, who was the nephew of the architect Domenico Fontana, was then commissioned to redesign the fountain. He built a base for the fountain on top of which a large basin was placed. The basin is decorated with steps and small columns. Maderno kept the large lower stone vasque of the old fountain, and decorated the pedestal on top of it with four stone scrolls. He removed the smaller upper vasque, and replaced it with a mushroom like shape with stone scales. When the water flows from the top it pours down over the upper vasque.
The fountain on St. Peter's Square had no pumps and operated by gravity, as all fountains built at the time. The source of water for the fountain was on a hill. This meant that the fountain could shoot water upwards into the air by depending solely the power of gravity.