Note 63

The only superficially similar alternation of chapels vaulted separately and chapels vaulted, Soissons fashion, under one keystone with the adjacent sector of the outer ambulatory can be observed in Chartres, where this arrangement is motivated by the necessity of re-using the foundations of the eleventh-century choir with its three deep and widely separated chapels. But in Chartres the Soissons-like chapels are really nothing but shallow protuberances of the outer ambulatory, so that all the seven keystones could be placed on the same perimeter. In Villard de Honnecourt’s and Pierre de Corbie’s ideal plan they are fully developed units, their keystones placed, not in the center but on the periphery of the adjacent sector of the outer ambulatory.