Torre Lapi (the Lapi Tower) is part of the Municipal building and it doesn't seem to be a gentle tower. Some scholars suppose it is part of the ruins of Porta Nova, one of the ancient walls that surrounded the city during the High Middle Ages. The tower was supposed to be located in the first circle. It was originally built as a passage, then the Lapi family bougth it from the Laigoni family and had it rearranged for personal needs. In the 15th century, they sold the tower for 400 lire to the Municipality of Bologna that wanted to enlarge the municipal building.
Later, it became part of the Municipal wall (it didn't differ a lot from what we may see today). It was used as a residence by many people: some Dominican monks, a painter, a family of beccai (the term was used in Bologna to refer to butchers. The origin of this name derives from the Becco, the male goat, the kind of meat people used to eat at the time). Their presence in this area wasn't accidental: from the mid-14th century the entire via porta Nova, now known as Via IV Novembre, hosted people who sold meat, once located in Piazza Maggiore. The new owners, the butchers, decided to change the features of the base of the tower, by opening their shop. But in 1505 the members of the Bolognese Senate decided to remove all the stands and shops that bothered them and make the whole area dirty. Probably, the explosion of the area during the 1641 fire was avoided thanks to this decision. The fire burst in the area where Agresti Tower is located and threathened the surrounding area as well.
During the napoleonic period the tower was almost halved, from around 30 metres to 18, to become part to the rest of the walls. In 1948 the ancient door of the beccheria was reopened to facilitate the entrance to the municipal building, even giving up again the original aspect of the tower.
Source:Bologna la selva turrita (in Italian) enhancement project of the historical-architectural Bologna's heritage supported by the Fondazione del Monte.