Rome is studded with cannon balls (2022)
essenceofrome.com
essenceofrome.com
Echoing another comment, before unification, Italy (1860s) had its "warring states period".
The North were independent small monarchies, including the Savoia, from which came the unification push with the help of Garibaldi.
In center Italy the Church ruled with an iron fist. In fact, when Rome was besieged and the Church lost, all of Italy was excommunicated by the Pope. (They then bactracked on the policy once they saw people just kept going about with their lives).
In the South was a repressed agricultural state that was so terrible to live under people invented something even worse: the mafia. (This is also why so many Italian Americans come from the South - they were escaping in search of a better life).
A song (in Italian) somewhat about it: https://www.youtube.com/watch?v=poaPh00AmDQ
They are supposed to be from the Blood Bath that happened there in the 16th century when Swedes and Danes still enjoyed killing each other frequently, but no wall survives this long with a metal ball in it, hence that’s apparently a fake thing by some smart 18th century building owners.
It wasn't showing the wall where it had crashed through, it's showing where the ball has been mounted into the wall for display.
Not a surprise to see Rome have so many based on that.
Whenever I am in NYC, I play a game called find the bullet hole , which is startlingly easy to do.
Taking the stairs in my uncles building it was clear that there had been a (or several) running gun battles up and down the stair well, and the spalling from small calliber rounds is just ignored and left, even in plate glass or store fronts.It may have been placed there.