Torre dell'Arengo is located over Palazzo del Podestà. This area has always been a central point for the city trade, as here there used to be a lot of sellers, clients, beggars and even cheaters. Under the big vault, notary stands and the gallows could be found as well.
If you look at Palazzo Re Enzo from the centre of the square, the tower can be seen. The tower has never been resistant because of its thin walls and not deep basis. In the beginning, in 1200, it was just a little raised part. Later it was transformed into a real tower, after experiencing some renovation works including base consolidation, strenghtening and renovation.
Source:Bologna la selva turrita (in Italian) enhancement project of the historical-architectural Bologna's heritage supported by the Fondazione del Monte.