A book of stone

A significant example in the history of the stereotomy is provided by a special ‘barrel-vault’ stone device which created roofing for spiral staircases. Already known and used in the twelfth century, this surface was first mentioned in a treatise at the end of the fourth book of Le premier tome de l’Architecture by Philibert De l’Orme: among the various examples of spiral staircase there is the first reference to a spiral barrel vault as the Saint-Gilles screw or spiral staircase. The name of this surface derives from the presence of an example of vault roofing whose intrados is characterised by the above-mentioned surface at the Abbey of Saint-Gilles in France. Although the staircase was completed in 1142, long before the first rigorous formulations of stone-cutting, the excellence and accuracy of the construction ensured that the ‘vis de Saint-Gilles’ became consecrated as a vital stage of the pilgrimages made by stone masons’ corporations to visit the works of greatest importance for learning the art of stereotomy. Evidence of their visits is provided by the marks engraved in the side walls of the staircase left by members of the corporations.