Frederick Barbarossa’s imperial army encamped on the outskirts of Tortona, an ally of Milan. Already here, Frederick had the first inklings of how difficult it would be to besiege and capture the cities of Northern Italy. The siege was carried out using ladders, mobile towers, “gatti” (self-propelled shelters), ditches, tunnels, mangonels, and trebuchets. All this, however, required time, money, and technical skill. These latter skills, however, were not the imperial army’s strong point, but were instead the hallmark of the communal armies, which also included artisans and master craftsmen.
