d up a great part of the east and west arches. But, though the
shape of the clerestory makes it plain that a vault was never even
intended, it seems very unlikely that the north and south arches were
originally loftier than those east and west. If we suppose that they
were all originally designed and built of the same height, we shall find
a very plausible reason for the form which the present roof has taken.
In such a case the transept must have had a flat wooden roof, the
natural covering to a clerestory of such a design, and must have looked,
with its great width, very squat and low. But when the new and far
loftier nave was built, it, of course, became necessary to heighten the
western of the four arches supporting the tower, and afterwards to go
through the same process with regard to the eastern arch. At such a
time, when the choir was completed, the two arches east and west would
be much loftier than the two north and south. Before rebuilding the
tower it would naturally occur to the builders to raise the north and
south arches to a level with the others, and to do this it would be
necessary to raise the roof. In such a case it would be quite natural
for the builders to hit upon such a roof as at present exists. They
would have before them already the example of a wooden vault in the
nave, and for the sake of uniformity they would be inclined to make
their new roof as much like that vault as possible. Having the size and
height of their arch settled before they designed their roof, the roof
would of necessity be shaped to fit the arch, and this would be the most
convenient roof for the purpose under the circumstances. This theory
will explain why a new roof was required in the fifteenth century, and
it also helps to explain other difficulties. For example, it is hard to
understand why the transepts, being so wide, are not loftier, and why
their original design made a vault impossible. But if we remember that
they were originally additions to a much lower nave and choir, we shall
see that their architect, having determined on a plan of great width,
was in a difficulty. If he made his transepts much higher than his nave,
the effect, both inside and out, would be very irregular. If he made
them of the same height, and vaulted them, they would be far too wide
for their height. He therefore determined, we will suppose, to make a
wooden roof which would sacrifice as little of the height of his
transepts as possible, and