It was built during the 9th century as a palace chapel for King Alfonso II of Asturias and the church of San Salvador of Oviedo.

Apart from acting as royal chapel, the Holy Chamber was built to house the jewels and relics of the cathedral of San Salvador in Oviedo, a function it continues to have 1200 years later.

Consequently, the cathedral of Oviedo was also called Sancta Ovetensis;[1] owing to quantity and quality of relics contained in the Cámara Santa (English: Holy Chamber).

It consists of two overlapping aisles with a barrel vault; the crypt or lower floor has a height of 2.30 metres, and is dedicated to St. Leocadia, containing several tombs of other martyrs.

On the upper floor, the Camara Santa dedicated to St. Michael, was extended in the 12th century, elongating the central section to six metres.