The Church of San Julián de los Prados is the oldest and largest of the Pre-Romanesque buildings still standing. Built during the reign of Alfonso II the Chaste (791-842), it was dedicated to St Julian and his wife St Basilissa. In the year 896, it was donated to the Cathedral of Oviedo along ''with its palaces, baths and triclinia'' by Alfonso III the Great.
It has a Latin basilica ground plan with three naves, a transept comprising a large transversal nave, a triple apse with three square chapels covered with barrel vaults, a portico at the west end and side rooms.
Inside, the naves are separated by semi-circular arches on square pillars. The central nave is separated from the transept by a transverse arch on each side of which are two spaces with stone arches.
The naves and transept are covered by a wooden framework, while barrel vaults are used in the chapels. Above the central chapel, there is an enclosure with access from the outside through a mullioned window with three brick arches on two small marble columns.
The paintings tdecorating the stucco that covered all the interior walls and vaults are noteworthy, being derived from Roman decorative motifs, as are the blind arcade that runs along the central apse and the latticework closing off the window openings (only one of which is original).
