During the 12th and 13th centuries, for reasons that are still not entirely clear, an incredible number of towers were built throughout Bologna, making for an urban skyline that almost resembles modern-day Manhattan. Today, only 22 remain.

One of the possible explanations for the vertical construction craze is that rich families used the towers as a symbol of wealth and status, as well as for defensive purposes to guard their land. Some of the smaller structures were built as dwellings.

The exact number of towers built in medieval Bologna is not clear. It was suggested that up to 180 towers were present in the city as of the 13th century, but a more realistic amount is probably around 100, which is still very impressive considering how difficult it was to build such tall structures with the limited resources of medieval Italy.

After the 13th century, some towers were demolished, others collapsed, and many were destined to different uses, such as residential or commercial buildings, or as prisons. The last demolitions occurred in the early 20th century, along with the 14th-century city walls.

Of the towers that remain today, the most famous are the Two Towers: the 320-foot Asinelli Tower and the truncated Garisenda Tower, both of which are leaning.