Each fountain in Rome is not on a square, but there is not a square without a fountain. Square or ital. Piazza is the core of the social life of Rome.
The Piazza Navona square lies on the old Domitian’s hippodrome (85 AD), which used to have an auditorium for 30,000 spectators. The Roman Stadium used to be a venue for athletic events and equestrian competitions (Lat. Agones), so the stadium used be called Circus Agonalis. Through the Middle Ages, the name changed from agone to navone, and later into navona.
Pope Innocent X organized a tender for the construction of the fountain because Caracalla‘s obelisk required a proper setting when they dragged it from Via Appia.
Bernini was not even part of the tender. Prince Niccolò Albergati Ludovisi, husband of the Pope’s niece, devised a cunning plan to include Bernini in the game.