Porta Castiglione could be called the “Gate of canals” (“Porta dei canali”) because next to it, there was a canal that allowed the Savena river to enter into the town. Waters of Savena were supplying hydraulic energy to dozens of mills that were producing silk and wool. The gate was built in the 13th century and rebuilt in the 14th century, exactly in 1378, 1379 and 1403. Its present aspect is the result of restoration works carried out by the Comune (city council) in 1850. The gate Castiglione was not mentioned in Descriptio of the cardinal Anglico from 1371, probably because it was not used in that period.
Source: "Restauro delle porte di Bologna 2007-2009"