A louvre is a small opening used for the passage of light or air in confined spaces. It can often be found in fortified buildings but also in strategic underpasses or on patrol paths, where it was used as a way to attack the enemy and still remain protected and covered. Because of this feature, louvres can be named after the weapon that was used. In the Cefalù Cathedral, the presence of louvres in the towers is characteristic of its defensive nature and fortress-like structure, typical of the Ecclesia Munita, commissioned by Roger II.