The quarries round St. Leu d'Esserent were noted, and many a church of France has been made of their firm white stones. The origin of Gothic art is comprised, thinks M. Lefèvre-Pontalis, in this region where good quarries abounded, with Senlis taken as a center. A line from Senlis to Laon, if carried round, would pass through Rheims, Provins, Montereau, Étampes, Vernon, Amiens, Péronne, St. Quentin. Well within that circumference lies St. Leu d'Esserent. The Benedictine church stands on prominent foundations overlooking the river loved of Corot and Daubigny. The priory was founded and presented to great Cluny by a knight of Esserent as thank-offering for his ransom from the Saracens by monks of St. Benedict. Of the church built in that XI century, there remain only the two stout columns, with archaic capitals, which now are embedded in the westernmost bay of the nave. About 1150 the present church was begun, and for a century continued building, in three distinct bouts of work. First was made the west façade, only one of whose Romanesque towers was ever finished with a spire, the octagonal faces of which were relieved by curious lancelike ridges not repeated elsewhere. In the narthex, or porch between the towers, was tried an experiment to eliminate the so-called domical shape of the first Gothic vaults. The transverse arches were loaded with masonry to raise them to the vault's apex. Experimental also are the ungainly diagonals, in part ornamented with Norman chevrons, that span the tribune over the forechurch (c. 1150). The ribs are not free of the vault web, so elasticity is missing. During the last quarter of the XII century, the chevet was built, as were the two towers placed beside the apse, an arrangement derived from Rhenish churches. Of that time, too (c. 1180), is the double bay, surmounted by a sexpartite vault which precedes the apse. There is no transept. The recently finished choir of Senlis Cathedral influenced the ambulatory and apse chapels of St. Leu. At Senlis and here occur the earliest examples of double flying buttresses. The six bays of the nave were added about 1220, after a pause in the works. Previously, each bay of the church had been lighted by a single lancet; now two lancets surmounted by an oculus were used, which added much dignity to the exterior aspect of the edifice. Over the axis chapel was built a second story. The unvaulted tribunes, above the side aisles, were transformed into a sort of triforium by building a wall slightly behind their arcaded openings. As that wall was pierced by some odd little square windows, this may be regarded as one of the first essays of a glazed triforium, the feature which was soon to develop into the decorative richness of St. Denis, Troyes, Le Mans, Tours, and Beauvais. CHAPTER IV Notre Dame of Paris and Other Churches of the Capital[71]