The fountain in this square was originally the fountain of the Acqua Pia (connected to the aqua Marcia aqueduct), commissioned this site by Pope Pius IX in 1870. Completed in 1888, it originally showed four chalk lions designed by Alessandro Guerrieri. These were then replaced in 1901 with sculptures of Naiads by Mario Rutelli from Palermo, the great-grandfather of the politician and former mayor of the town, Francesco Rutelli.
The naiads represented are the Nymph of the Lakes (recognisable by the swan she holds), the Nymph of the Rivers (stretched out on a monster of the rivers), the Nymph of the Oceans (riding a horse symbolising of the sea), and the Nymph of the Underground Waters (leaning over a mysterious dragon). In the centre is Rutelli's Glauco group (1911/12), symbolizing the dominion of the man over natural force and replacing a previous sculpture.