Begun ca. 1200
A five-aisled basilica, with side aisles that are the same height, intersected by a shallow transept, terminated in the east by an ambulatory surrounded by a ring of nine spacious radiating chapels. The axial chapel projects more deeply than the other radiating chapels. The chapel at the base of the ambulatory is diagonally placed as at the abbey church at Orbais.
Three story elevation throughout with an arcade sitting on compound piers, glazed triforium, linked to tall clerestory. The ubiquitous use of deep coloured glazing lends unity to the interior space. The elevation is a modest one - a double square 48 meters high by 48 meters wide.
Work began soon before 1200 on the base of the hemicycle. In 1208 the old Roman wall was demolished allowing construction of the axial chapel. Work was under way of the upper stories when in 1228 a powerful wind storm damaged the building. When work resumed in the 1230?s in the upper stories of the triforium and choir the work was under the direction of a master mason from the Île-de-France. Work progressed from east to west, however a lack of funds and disasters prevented completion of the nave until 2nd half of 15th-century. One of the great master masons of late French gothic - master Bleuet from Reims, contributed to the design of the western frontispiece in 1455. The western frontispiece dates from 1500-50 which was initially under the direction of master mason Martin Chambiges (d.1532).
Work begins in local style with links to Reims, Meaux, Orbais, Lagny. However this work was over laid in the 1230?s in a Parisian mode bringing the tall clerestory windows. The well documented late gothic campaign provides a multitude of insights to the business of cathedral building. The western frontispiece may be understood as the last expression of french flamboyant architecture.