If two of the three miracles required to become Saint must be done while alive, it follows that many of the remaining third (the post-life miracles) of Christianity probably took place in Rome since Saints lived everywhere throughout Christendom, but once dead were often brought to Rome for veneration.
All those (900?) churches in Rome? Each one is dedicated to a different saint and containing either their body or a related relic. Believers coming to Rome throughout the ages would pray in those churches for intercession by those saints …ergo, high concentration of miracle probability simply given the sheer volume of acts of faith in Rome over time.
Just a theory. We haven’t run the exact numbers but… miracles of all types certainly do abound in Rome. One took place in 1849 at San Bartolomeo all’Isola, (lit. “on the Island”). Of course, as one of the 12 apostles Saint Bartholomew had already been saint for quite some time, so this miracle was probably just added to his already long list, many of which for some reason have to do with weight… heavy objects becoming light and vice-versa and such.
This miracle is no exception. During mass one day the church was full of the faithful. The French pro-Papal forces fired yet another cannon fusillade upon the pro-Republican city from the Gianicolo hill about a mile away. (Romans to this day still call cannonballs “Pius 9ths”, after the Pope at the time.) The cannon ball came arcing through the sky right towards the church. But instead of demolishing the church and causing a tragedy inside, the cannon ball sailed through a small window and simply yet miraculously lodged itself in the wall by the altar, visible for all to see to this day.