- The Fountain of the Four Rivers -

The three fountains, fed by the Aqua Virgo aqueduct, are the main decorative elements of the piazza. The most remarkable of these, la Fontana Dei Quattro Fiumi (Fountain of the Four Rivers) is an expression of Bernini's most consummate artistry.

Innocenzo X wanted a monument that would form a centerpiece for this elongated space but not disrupt its unity. An obelix from the circus of Maxentius was erected over a rocky grotto, from which a lion and a horse are to be seen emerging. The hieroglyphics give an official version of Domitian's coming to power in 81 AD.

The fountain is all the more impressive because the obelisk appears to be resting on a open cavity; in this Bernini achieved a remarkable tour de force that gives it a sense weightlessness. The large figures reclining precariously on the rocks above the glistening water represent the main rivers of the four continents: the Danube, the River Plate, the Ganges and the Nile, (with a veiled head to indicate that its source was still unknown at that time). All around the monument, and also on the tip of the obelisk, the Pope had his family crest sculpted: a dove holding an olive branch.

The other two fountains, the basins of which were made in the 16th century to designs by Giacomo Della Porta, only took on their present appearance in the19th century. Their light-colored stone illuminates the piazza. At the southern end, the figured of an Ethiopian hunting a dolphin that dominates the Fontana del Moro is a copy of a statue designed by Bernini.

The surrounding by Della Porta, the originals of which are now in the Giardino del Lago of the Villa Borghese, have also been replaced by copies. The ornaments of the Fountain of Neptune, at the north end of the piazza, were added in 1873.