Between the 12th and the 13th century, the number of towers in the city was very high, possibly up to 180. 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.
Besides the towers, one can still see some fortified gateways that correspond to the gates of the 12th-century city wall which itself has been almost completely destroyed.
During the 13th century, many towers were taken down or demolished, and others simply collapsed. Many towers have subsequently been utilized in one way or the other: as prison, city tower, shop or residential building. The last demolitions took place during the 20th century, according to an ambitious, but retrospectively unfortunate, restructuring plan for the city.
Of the numerous towers originally present, fewer than twenty can still be seen today. Among the remaining ones are the Azzoguidi Tower, also called Altabella (with a height of 61 m), the Prendiparte Tower, called Coronata (60 m), the Scappi Tower (39 m), Uguzzoni Tower (32 m), Guidozagni Tower, Galluzzi Tower, and the famous Two Towers: the Asinelli Tower (97 m) and the Garisenda Tower (48 m).