In the centre of the piazza, immediately opposite the church, Bernini erected for Innocent X the Fountain of the Four Rivers. The obelisk of red Oriental granite which surmounts it was brought from the Circus of Maxentius, and tipped with the bronze dove and olive-branch, the emblem of the Pamphili family, to which Innocent X belonged. Bernini placed the obelisk on four flying buttresses of white granite, crossing each other at right angles. The obelisk rests upon the arch thus formed, and the space beneath it is left as a grotto with four openings. This gives the obelisk the appearance of resting upon nothing, an effect which was greatly admired by the artist’s contemporaries. The bases of these flying buttresses are broadened and flattened so as to receive the recumbent figures of four river-gods carved in Carrara. They represent respectively the Ganges, the Nile, the Danube, and the Rio de la Plata. The obelisk and its base stand in the centre of a basin some seventy-eight feet in circumference, which is sunk into the pavement, and which receives the water flowing from the four rocky projections where the river-gods lie. Beneath the grotto additional jets of water spout upward, while a river-horse dashes furiously through one archway as if in terror of a lion which is coming out of another to drink of the water under the shade of a palm-tree cut in high relief against the rocks. On top of one of the rocks crawls a serpent, and a mass of cactus grows upward from behind one of the rivers. In the lower basin two monstrous travertine fish are disporting themselves in characteristic Bernini contortions. Escutcheons bearing the arms of Innocent X (three fleur-de-lis and a dove with an olive-branch) of course are not wanting. All this sculpture is in travertine.