A masterpiece sculpture of Mannerism style, the result of the chisel of the Flemish sculptor Giambologna, it was built between 1563 and 1566 to glorify the Papal State of Pope Pius IV and to represent the Church's political power over the city of Bologna.
The sculpture was created in Bronze, inside a marble reservoir, although conceived for purely ornamental purposes, due to the inscription "Populi Commodus" placed on one of the sides at its base, it was used in the past by merchants to wash vegetables and by laundresses to do the laundry.
It represents the ancient divinity, God of the waters and symbolically refers to the power that, having descended from the throne, dispenses wealth and fertility.
Around the tank, there are four Nereids (sea-nymphs) holding their breasts and four cherubs holding dolphins symbolizing the 4 most important rivers of the world known at the time: the Danube, the Ganges, the Nile and the Amazon.
The fountain has many nozzles incorporated in the various bronze figures. It was initially fed by an underground conduit coming from a spring located near the hill of San Michele in Bosco. This conduit still exists and can be accessed by booking a guided tour.
On the base of the fountain are indicated four Latin inscriptions that indicate the purposes for which the work was created: FORI ORNAMENTA (to honor the square), AERE PUBLICO (built with the citizens money), POPULI COMMODO (made for the use of the People), MDLXIII (built in 1564).
According to the Bolognese tradition, the Flemish artist would have liked to make the statue with larger genitals, but the Church objected. Not accepting this decision, the sculptor modified the pose and angle of the thumb on the left hand, making it allude to an erect penis.
Neptune's trident also inspired the well-known Bolognese car manufactures, the Maserati brothers who used it as the logo for their Company and it can be found on the hood of every one of their cars.