The exterior affords many features of interest. It is, as I have said, almost entirely round-arched, and the choir affords a good example of the triple division in height, rendered necessary by the groined triforium and the projecting chapels of the apse. The clerestory and triforium are each lighted with one window in each bay, whilst the chapels have three windows,--a wide one in the centre, and a much smaller one in each side. There are no flying buttresses to the clerestory, but small quasi-buttresses, formed of three-quarters of a shaft, finished under the eaves with a conical capping. The eaves cornice all round the church, of intersecting round arches, resting on corbels, is so similar in its character to some of the work in the beautiful chapter-house of S. Georges de Boscherville, that I can hardly doubt that they were executed under the same influence, if not even by the same workmen.
The feature, however, which lends the most interest to the building and aids so much in its picturesque effect externally, is the grand Lady-chapel,[21] said to have been built by the Abbot, Peter de Wesencourt, between the years 1259 and 1266. In plan, disposition and general arrangement it appears to be as nearly as possible identical with the destroyed Lady-chapel of S. Germain-des-Prés at Paris, built by the celebrated Pierre de Montéreau, between the years 1247 and 1255. Pierre de Montéreau built also the S. Chapelle at Paris, between 1241 and 1248, and died on the 17th March, 1266. A comparison of the design of these three buildings has induced me to believe that in this Lady-chapel of S. Germer we have another genuine work of this great architect, for it was built before his death, and is identical in many of its features with work which we know to be his. The plan of all these buildings is identical.[22] They all had two staircase turrets and a large rose-window at the west end, a parapet above the rose-window, and a smaller rose in the otherwise plain gable. The design of the window tracery, the gables over the windows, the detail of the staircase turrets, buttresses and parapets, are all so similar that my suggestion really scarcely admits of a doubt. The main differences are, that at S. Germer the original western rose-window is perfect, whilst in the S. Chapelle it is a flamboyant insertion, and that the chapel is of one story in place of two. In this last point, and in its complete separation from the church, it agrees entirely with the destroyed chapel at S. Germain-des-Prés. The passage between the apse and the chapel is of three bays, with a doorway at the side, but, so far as I could see, no trace of an entrance from the apse. It is groined: the windows (of four lights) are much elaborated with mouldings, and have trefoiled inside arches: and an ascent of six steps leads from it under a fine archway into the chapel. There is a north doorway in the chapel, and the whole is groined. The dimensions appear, as nearly as I can make out, to be precisely the same as at S. Germain, but less than in the S. Chapelle, being about twenty-seven feet six inches in the clear between the groining shafts, and between seventy and eighty feet in length. The original altar of stone, supported on a trefoiled arcading, remains fixed against the east wall. This is six feet five and a quarter inches long by three feet three inches high. In the museum at the Hôtel Cluny, at Paris, one of the most valuable relics is a stone retable, painted and gilded, formerly in this chapel. I have not its dimensions, but it is of much greater length than this altar, and I have no doubt, therefore, that the principal altar stood in its proper place under the chord of the apse, and that the retable belonged to it. This arrangement was not uncommon; it was identical with that of the altars in the S. Chapelle, the same arrangement existed originally at Amiens; and we have an instance of it in England in the choir of Arundel church.