buttresses meet, at the level of the triforium and above the
clerestory windows, the thrusts of the upper walls.

The plan is most curious, and on account of its irregularity as well as
certain inconsistencies, it is difficult to guess how far it was
originally conceived in its present form, or what alterations were made
in the earlier centuries. Some changes must have been made in its
vaulting. The chevet or Capilla Mayor, which at first very properly
contained the choir, is surrounded by a double ambulatory, outside of
which the thick walls are pierced by nine apsidal chapels. It is
probable that these were originally constructed by the engineers to
lighten the enormous bulk of the outer masonry. They are not quite
semicircles in plan, and are vaulted in various simple ways. Where ribs
occur, they meet in the key of the arch separating chapel from
ambulatory. The piers round the apse itself are alternately
monocylindrical and composite; the intermediate ones, subdividing
unequally the "girola," are lofty, slender columns, while those of the
exterior are polygonal in plan, with shafts against their faces. Some of
the caps are of the best Romanesque types, and composed of animals,
birds, and leaves, while others, possibly substituted for the original
ones, have a plain bell with the ornamentation crudely applied in color.

The Capilla Mayor has both triforium and clerestory of exquisite early
work. Dog-tooth moldings ornament the archivolts. Mohammedan influence
had asserted itself in the triforium, which is divided by slender shafts
into two windows terminating in horseshoe arches, while the clerestory
consists of broad, round, arched openings.

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 gir