These mini castles were built all over the city.
The reasons for the construction of so many towers are not clear. One hypothesis is that the richest families used them for offensive/defensive purposes during the period of the Investiture Controversy.
Only a few survive to the current day.
https://en.m.wikipedia.org/wiki/Towers_of_Bologna https://www.sciencedirect.com/science/article/pii/S1296207418306952
i guess it’s sad, but by the time photography came around, they had been silly and useless already for hundreds of years… nobody needed them for anything, and they were always at risk of just toppling over… the rich families spent years and years building useless vanity projects that would eventually just crumble on top of the heads of people living down on the street…