The surviving elements of the original structure include the general arrangement of the interior: three naves separated by three ultra-semicircular arches over Corinthian capitals, and the apse formed of a single rectangular chapel. The many geometrical decorative elements are also original and more numerous than those of any other Iberian monument of the period. The interior is divided into three sections supported by three arcs, supported by cylindrical columns, with polymorphic capitals. A triumphal arch divides the chapel from the main altar, while the roofs are supported by beam timbers. The high altar is decorated in a carved-wooden retable, gilded in gold, with an image of Saint Peter over the altar. The naves on either side of the main altar are decorated with carved-wooden chapels covered in gold.