The construction and balance of the apse thrusts were doubtless originally of a somewhat different nature from what we find at present, as may easily be observed from the materials, the function and positions of the double flying buttresses. They may have been added as late as three centuries after the original fabric. Lamperez y Romea's observations in regard to this are most interesting:-- "We must observe in the two present orders of windows, that the lower was never built for lights and its construction with double columns forming a hollow space proves it a triforium. That it was actually so is further abundantly proved by several circumstances: first, by a parapet or wall which still exists below the actual roof and which follows the exterior polygonal line of the girola, as well as by some semi-Romanesque traceries which end in the wall of the Capilla Mayor, and finally, by a continuous row of supports existing in the thickness of the same wall below a gutter, separating the two orders of windows. These features, as well as the general arrangement of the openings, demonstrate that there was a triforium of Romanesque character, occupying the whole width of the girola, which furthermore was covered by a barrel vault. Above this came the great platform or projecting balcony, corresponding to the second defensive circuit. Military necessity explains this triforium; without it, there would be no need of a system of continuous counterthrusts to that of the vaults of the crossing. If we concede the existence of this triforium, various obscure points become clear." The Capilla Mayor has four bays prior to reaching the pentagonal termination. The vaulting of the most easterly bay connects with that of the pentagon, thus leaving three remaining bays to vault; two form a sexpartite vault, and the third, nearest the transept, a quadripartite. All the intersections are met by bosses formed by gilded and spreading coats-of-arms. The ribs do not all carry properly down, two out of the six being merely met by the keystones of the arches between Capilla Mayor and ambulatory. The masonry of the vaulting is of a reddish stone, while that of the transepts and nave is yellow, laid in broad, white joints.