The first thing that strikes the visitor upon entering is the enormous size of the windows, which occupy the entire space between the buttresses, and rise to the base of the roof. All the weight of the vaulting rests, therefore, upon the exterior buttresses, but not the slightest inflection has ever taken place. The church is built truly east and west, the entrance to each chapel being by separate portals. The only modification the exterior of the building has sustained since S. Louis' time is the addition of a little oratory attributed to Louis XI., and the rebuilding of a part of the _façade_ in the 15th century.
The porch of the lower chapel is divided into two bays by a pier, on which is a statue of the Blessed Virgin, while above in the tympanum, is a representation of the _Coronation of the Virgin_. The restoration of this and the entire ornament of the doorway is the work of M. Geoffroy-Dechaume. The original statue had the reputation of working miracles; and it is related that when, towards 1304, Jean Duns Scotus, a celebrated theologian of the University of Paris, was praying at its feet, it bent its head in approval of the doctrine of the Immaculate Conception, which that learned doctor was teaching. It has since always remained in the same position. The portal of the upper chapel is of the same character as the lower one, but richer in its decoration. It is nearly all new, for the old ornament had not only been mutilated, but had been completely chiselled off. The _voussure_ is a mass of sculptures--single figures, groups, and ornament. The figures are forty-four in number: Angels carrying the elect to heaven, Angels censing and bearing crowns, martyrs with the instruments of their sufferings, and the lost souls surrounded by the flames of hell, the whole forming a framework to the central subject in the tympanum, the _Last Judgement_; the work is a marvel of patient study, modelled upon the portals of Notre-Dame and S. Germain l'Auxerrois, each figure having been fitted into its place upon the lines of the original wherever any traces of the old sculptures had been preserved.
The plan of the church is a parallelogram, terminating in a polygonal apse. The buttresses reach to the parapet, and terminate in pinnacles surrounded by gargoyles ornamented with the most grotesque birds and beasts. The windows of the nave are divided into four lights, with foliated circles in the heads very similar to those of the Chapter House at Salisbury. Several _flèches_ have preceded the present one; the first fell in the reign of Charles VI., the second was burnt in the great fire of 16th July, 1630; the third was erected by Louis XIII. in the ogival style of that period, and remained until the 17th century. When it was destroyed, in 1791, it contained five bells, which had been cast in 1738; the Dauphin, the Duc d'Orléans, the Duc de Chartres, and the first President of the Chambre des Comptes being their sponsors. The present _flèche_ was erected in 1853, and is in the style of the 15th century. It is of wood, covered with lead, and consists of three octagonal storeys supporting the spire.