The building has suffered so much from alterations over the centuries and only the general plan has been preserved. It is that of a basilica with nave and aisles divided by rude stone piers set at unequal intervals, from which round arches spring. In the easternmost bay, however, owing to the smaller span, the arch was made sufficiently pointed to raise its crown to the same height as the others. This irregularity was already typical of Imperial Roman times, when barrel vaults were given a pointed form in order to make the height of rooms of varying size uniform, as it was necessary to raise the crown of the vault in some of them. This is illustrated by various chambers in the
House of Tiberius on the
Palatine. There is no satisfactory explanation of the "many angels" the building is said to have presented in the
Codex Vigilianus. In the rectangular sanctuary atriplet round-arched window ( is preserved. With its pre-romanesque bases, rough brick arches, and capitals with rude packed leaves, it gives an idea of the better style of building and carving in the time of
Alfonso II of Asturias. It is known that the church of San Tirso housed Royal Chapel. == See also ==