Two fountains form the axis of the piazza.

Designed by Maderno in 1613 and set to one side of the obelisk, making a line parallel with the basilica’s facade. Bernini's plan uses this horizontal axis as a major feature of his unique, spatially dynamic and highly symbolic design. The most obvious solutions were either a rectangular piazza of vast proportions so that the obelisk stood centrally and the fountain (and a matching companion) could be included, or a trapezoid piazza which fanned out from the facade of the basilica like that in front of the Palazzo Publicco in Siena.