To compete with Bologna's towers, the Comune added the characteristic octagonal cusp, designed by Arrigo da Campione, one of the numerous masters from Campione who took part in the cathedral's renovation in the 13th-15th centuries.
In order to surpass Bologna's towers, the Comune included an octagonal spire in the cathedral renovation project, designed by Arrigo da Campione and executed by other architects from Campione between the 13th and 15th centuries.