triangular bays and square chapels have stone roofs sloping down to a gutter between them; whilst the bay between them had a square roof sloping slightly all ways, and over the outer chapel a roof sloping back to the same gutter. The water is all carried away by stone channel-drains to the outside of the walls. The whole of this contrivance is now obscured by an extraordinary jumble of tiled roofs one over the other, added, I suppose, from time to time as the original roof required repair.[233] There are double flying-buttresses wherever there are transverse arches in the groining. These were altered in the fifteenth century by the addition of a fringe of cusping on the edge of their copings, which of course spoilt their effect, though this is not of much consequence now, as they are never seen. The nave also has double flying-buttresses; and its clerestory and triforium were thrown into one, and large windows inserted, in the fourteenth century in place of the original work. The only portion of the original external walls of the aisle that I could see was on the south side of the choir. Here in the apse chapels there are good and rather wide lancet-windows with engaged shafts in the jambs, well moulded, and labels adorned with dog-tooth. The old termination of the buttresses seems to be everywhere destroyed. The flying-buttresses in the apse were finely managed. Owing to the arrangement of the plan two flying-buttresses support each of the main piers, and they are double in height. Their arches are moulded with a very bold roll-moulding, with a smaller one on either side, and the piers which receive them are faced with coupled shafts with carved capitals. The arrangement of the buttresses follows exactly (and of necessity) the planning of the principal transverse arches of the groining. From each angle of the apse there are two flying-buttresses; these each abut against a pinnacle, which is again supported by two diverging flying-buttresses. It might be expected that the effect would be confused, as it is in the somewhat similar plan of the chevet of Le Mans; but here the buttresses and pinnacles seem to have been less prominent, and therefore to have interfered less with the general outline of the church which they support. The pinnacles to the buttresses of the central apse are tolerably perfect, but they appear to be not earlier than the fifteenth century. Those of the intermediate aisle are all destroyed, but many of those in the outer aisle still remain. The chapel of San Ildefonso, too, beyond the chevet, retains its pinnacles and parapets; and behind these rises a flat-pitched tiled roof, which, as everywhere else throughout the cathedral, has the air of being a modern substitute for the old roof: undoubtedly the whole work wants steep roofs to make it equal in effect to the French churches from which it was derived, and in which this feature is usually so marked.