The architecture of the church is of a remarkable beauty: the basilica floor plan is structured into three naves separated by semicircular arches resting on square-shaped pillars with impost capitals and a wooden ceiling. The transept is of striking dimensions and height, illuminated by the large opening in the southern wall and communicating with two adjacent spaces or sacristies in the north and south façades.

In the chevet, there are three chapels with vaulted ceilings and openings with lattices, and small shrines or tabernacles adjoining the back wall. The main chapel features blind arcades, and above there is a chamber of unknown purpose only accessible from outdoors through a bay with three semicircular arches supported on columns with capitals, which is typical of pre-Romanesque architecture in Asturias.

The decorative program consists of exceptional sculptures and paintings, and its relevance for the celebration of ceremonies before the king left for battle and after his return has also been underscored.

The sculptural decoration is concentrated in the holiest space, in the blind arcades of the Main Chapel, featuring many reused pieces: capitals, base, shafts and pilasters of Roman and Visigothic traditions with exceptional contours and quality.

The frescoes with clear classical roots feature a marvellous array of plant motifs and geometric and architectural motifs, together with the image of the True Cross, depicted again and again over the expanse of the walls.

This is a complex symbolic universe that refers to the Celestial Jerusalem inspired in the St. John’s vision in the Book of the Revelation or Apocalypse: “(…) its wall was made of jasper, and the city of pure gold, as pure as glass. The foundations of the city walls were decorated with every kind of precious stone. The first foundation was jasper, the second sapphire, the third agate, the fourth emerald, (Ap. 21, 18-19).

The current state of the building is the result of work carried out by the researcher and philanthropist Fortunato Selgas and the architect Vicente Lampérez in the years 1912-1915. The work of these experts restored the original architectural configuration of the building, while eliminating additions from the Baroque and rough plaster coats on the interior walls, which led to the discovery of the ensemble of paintings from the High Middle Ages, among the most important from the High Middle Ages conserved in Europe.

San Julián de los Prados continues to operate as a parish in the present day.