The fountain at the junction of three roads marks the terminal point of the "modern" Acqua Vergine, the revivified Aqua Virgo, one of the ancient aqueducts that supplied water to ancient Rome. In 19 BC, supposedly with the help of a virgin, Roman technicians located a source of pure water some 13 km (8 miles) from the city. (This scene is presented on the present fountain's façade.) However, the eventual indirect route of the aqueduct made its length some 22 km (14 miles). This Aqua Virgo led the water into the Baths of Agrippa. It served Rome for more than four hundred years.The coup de grâce for the urban life of late classical Rome came when the Goth besiegers in 537/38 broke the aqueducts. Medieval Romans were reduced to drawing water from polluted wells and the Tiber River, which was also used as a sewer.
The Roman custom of building a handsome fountain at the endpoint of an aqueduct that brought water to Rome was revived in the 15th century, with the Renaissance. In 1453, Pope Nicholas V finished mending the Acqua Vergine aqueduct and built a simple basin, designed by the humanist architect Leon Battista Alberti, to herald the water's arrival.

In 1629 Pope Urban VIII, finding the earlier fountain insufficiently dramatic, asked Gian Lorenzo Bernini to sketch possible renovations, but when the Pope died, the project was abandoned. Bernini's lasting contribution was to resite the fountain from the other side of the square to face the Quirinal Palace. Though Bernini's project was torn down for Salvi's fountain, there are many Bernini touches in the fountain as it was built. An early, striking and influential model by Pietro da Cortona, preserved in the Albertina, Vienna, also exists, as do various early 18th century sketches, most unsigned, as well as a project attributed to Nicola Michetti one attributed to Ferdinando Fuga and a French design by Edme Bouchardon.