The Cannonball Fountain (Fontana della Palla di Cannone) can be found in the Viale della Trinità dei Monti in front of the Villa Medici, in Rome. The cannonball is supposed to have been a “gift” of an angry Queen Christina of Sweden.
Cannonball Fountain Rome
Address, opening hours and entrance fee

Address: Viale della Trinità dei Monti, 1 – Rome. The fountain can always be seen from outside.
History and description
The Cannonball Fountain was constructed in 1589 by Annibale Lippi, who built it for Cardinal Ferdinando Medici. The monument is characterized by an octagonal basin, with a central pillar. The pillar supports the circular shell holding the cannonball.
The basin had been acquired by the cardinal from the convent of the San Salvatore in Lauro Church.
The cannonball is supposed to have been a substitution for an iris (a symbol of the Medici).
If you look very carefully, you can see a round imprint in the main door of the villa. Queen Cristina of Sweden is supposed to have once thrown the white marble sphere resting in the granite cup at this door. According to another story she is supposed to have shot a cannonball at the Villa, from the Castel Sant’Angelo. This is a distance of 1,5 kilometres and the Queen lived in the 17th century, so the story is cute, but likely to be a bit of an exaggeration.
The fountain is not to be confused with the Fountain of the Cannonballs (plural) near Castel Sant’Angelo.