Around 1200 AD Bologna was one of the 10 biggest cities of Europe thanks to the old famous university and had around 100 towers as a demonstration/challenge of status between most important families (just like today in Manhattan, see American companies or men like Trump, Rockefeller..) and as defense purposes because of the civil war between Guelph (oversimplifying: papal) and Ghibelline (oversimplifying: imperial) families, which often resulted in murders. Also attack purposes sometimes: hit a passerby in the street from above with arrows or boiling oil and take refuge inside. A civil war in a small city is no joke.
Today around 30 towers remaning, not a bad result in around 800 years.. some of them you can still climb. Some others were demolished, others felt in centuries (oh yeah, some killing people). In the second pic you can see the most famous 2:
Asinelli Tower is our pride: built in 1120 AD, 100 meters (320 ft), today still the highest medieval tower existing of the world (as an example, the first time a US skyscraper exceeded 100 meters - 320 ft was only in 1890 AD, 770 years later), was probably the highest tower of the world of its time. Garisenda Tower, the smaller tower of the two, less famous but more leaning than Pisa Tower and much older (1110 AD vs 1373 AD, so older than Gengis Khan for example) & in peril of fallin' down but under restoration. That pic doesn't do it justice:
