The fountain in the Piazza Colonna is a fountain in Rome, Italy, designed by the architect Giacomo Della Porta and constructed by the Fiesole sculptor Rocco Rossi between 1575 and 1577.The fountain was one of a group of sixteen fountains built by Della Porta following the reconstruction of the Acqua Vergine aqueduct, a project begun by Pope Pius IV in 1561 and finished by Pope Pius V in 1570. The fountain itself was built under Pope Gregory XIII, best known for creating the Gregorian calendar.