It is clear that from the
outset the idea of covering the cathedral with a stone vault was abandoned.
This is evident from the insubstantial nature of the separations between
the nave and side-aisles, the absence of buttresses and the insufficient
thickness of the outer walls also point to this. Therefore, in all certainty
the original roof was made of timber –the nave having a gabled roof
and the lower side-aisles single slope roofs. The whole design being in
keeping with the form of classical Roman basilicas.
Over time, changes were made due to damage
to the roof of the cathedral caused by a number of fires. Around 1520, the
side-aisles were covered with ribbed vaulting, designed by Juan Segura.
The ribbed vaulting of the nave was designed by Juan de Bescós in
1598 and the, unfortunate, reforming of the central apse was undertaken
in 1790 and decorated with frescos by Friar Manuel Bayeu.
However,
the ceiling of the transept is the original one. It is a barrel vault perpendicular
to the axis of the nave, and with the transept crossing, as already mentioned,
covered by a magnificent and innovative dome erected over four transverse
arches and four squinches.