The famous fountain dei Fiumi (of the rivers) is situated at the centre of the square that in the ancient times was occupied by the Stadium of Domitian. It is fed by the Acqua Paola and was inaugurated on 12 June 1651 by Innocent the Tenth Pamphilj (1644-1655). 

The work was done by Gian Lorenzo Bernini, whose project was preferred to the simpler one presented by his famous rival Francesco Borromini. The obelisk coming from the Circus of Maxentius on the via Appia rises at the centre of the fountain, almost suspended over the cavity below. 

At its feet a high rocky base hosts four gigantic statues sculpted by Bernini’s collaborators that represent the rivers of the four continents known at that time: the Nile, symbol of Africa, work by Giacomo Antonio Fancelli; the Ganges, symbol of Asia, work by Claudio Poussin; the Danube, representing Europe, by Antonio Raggi, and the Rio de la Plata, representing America, by Antonio Francesco Baratta. 

The Nile has the particularity that the head is veiled, alluding to the fact that the location of its springs was still unknown in the seventeenth century, while the Rio de la Plata presents coins scattered on it side, symbol of the richness of the American territories. The cliff is rich in flowers, fruits, animals. A snake is placed on the top of the base, the foliage of a wonderful palm-tree seems to be swept by the wind, a horse and a lion come out of the rocky cavity, while two dauphins are immersed in the circular basin. 

The coat of arms of the Pamphilj family, a dove with an olive branch in its beak decorates the sides of the base and the top of the obelisk. Some attitudes of the representations, in particular of the Rio de la Plata, with its scared expression and the left hand raised as if to defend itself from the collapse ofthe nearby church of Sant’Agnese in Agone, have excited the imagination of the people generating anecdotes on the rivalry between Bernini and Borromini. These anecdotes are pure fantasies, because the works for the construction of the church had not even started when the fountain of the Rivers was already completed. 

The high costs for the construction of the monument caused a strong discontent by the people, burdened on that occasion by a new tax on bread, against Innocent the Tenth and his sister-in-law, the ambitious Olimpia Maidalchini. Furthermore the market that had been kept in this square since 1477 was forced to change place, to make room for walks and meditations, as commemorated by an inscription on a side of the base of the obelisk. 

However small commercial activities managed to survive in the course of time in this wonderful scenario that the Pamphilj family had destined to become an absolute masterpiece of the baroque art. 

The custom of flooding the square in the sultry August days by closing the drains of the fountains datesback to the seventeenth century and lasted until 1867.