Cathar Wars - Medieval Warfare - Siege Towers (Belfries, belfrois)

The medieval belfry was not a church tower, but a siege engine - the modern meaning seems to have come about by the erroneous association of towers and bells (etymologically, the bel in belfry is not connected with the word "bell").

A belfry was used for gaining access to a castle, generally at the level of the battlements. It was typically constructed in wood, on several stories - as many as necessary to reach the battlements. Each story offered a location for attack - bows and crossbows in the lower levels, and armed men in the upper level, ready to drop a sort of drawbridge and gain access to the castle ramparts. The belfry was normally wheeled, so that it could be moved up against the castle walls, and like all exposed wooden engines of war it would be covered in the hides of freshly slaughtered animals and regularly dowsed in water to keep it fireproof.

A wheeled belfry with its own battlements

One way to foil the approach of a belfry was to have sloping castle walls. This forced the attackers to cover a greater distance from the top of the belfry to the top of the castle wall. This was one of the benefits of a talus. Another way to foil the approach was to build ditches and moats to prevent the approach of belfries. As on the right, attackers often needed to fill up the ditch or moat to provide a level surface that extended all the way to the foot of the castle wall. In practice, all sorts of material was used for this: earth, rocks, straw, dead bodies, wood, whatever came to hand. If too much wood was used in the infill then the infill itself became a target for fire setters.

A covered belfry crossing an infilled dry moat, with a boarding party crossing the lowered drawbridge