Rome Fell For The Last Time, This Day 147-Years Ago, Paving The Way For Italian Unification — September 20, 1870.
Rome, with the Pope & the Vatican right there, was the last holdout when it came to the by then inevitable unification of the Italy. Hence the significance of this day. Once Rome fell, 147-years ago the Rubicon had been well and truly crossed. Because of religious fervor the pope had to be appeased or at least humored. So, unification dragged onto 1871. But, the popes still claimed to be prisoners of the Vatican.