The nave of the prioral church of Saint-Leu-d’Esserent (Oise) has never been looked at as a subject per se. The study of elevation, modenature and sculptural decoration shows the combined influences of the great gothic cathedrals of Paris, Chartres and Soissons. It is now possible to consider that its nave was built around 1190-1200, in two construction sequences. The triforium, with piercing windows in its back wall, would then be one of the first examples of such a light-enhancing device.