The Arca Santa ("Holy Ark", or chest) is an oak reliquary covered with silver-gilt decorated in the Romanesque style. It is kept in the Cámara Santa of the Cathedral of San Salvador in Oviedo. In 1934 the Cámara Santa suffered an explosion that severely damaged the Arca, which was carefully restored by Manuel Gómez-Moreno.
The Arca is a black oak box 72 by 119 by 93 cm, which is unusually large for a reliquary, more typical of the size of a small portable altar. It was constructed without nails, perhaps in imitation of Solomon's Temple. The whole is covered in silver: front and both sides are repoussé, the back has a simple checkered pattern, and the flat lid is engraved with niello. Appropriately for its size, the front panel is modelled after an altar front, depicting Christ in majesty on a mandorla carried by four angels and flanked by the Twelve Apostles. The panel is bordered on all sides by a Kufesque inscription.
The left side is a narrative cycle of Christ's infancy in five scenes arranged in two registers, read counterclockwise from the top right. The two rows are separated by a band which reads: MARIA ET IOSEP POSUERUNT DOMINUM IN PRESEPIO ANIMALIU / ANGELUS APARUIT IOSEP DICENS FUGE IN EGIPTUM ET ESTO [IBI] ("Mary and Joseph put the Lord in the animals' manger / An angel appeared to Joseph saying, 'Flee into Egypt, and stay [there]"). The right side is also divided into two registers separated by a band of text. The top depicts Christ in a mandorla supported by two angels on the left and on the right Michael the Archangel, flanked by a cherub and a seraph, battling a dragon. The bottom row shows eight apostles in various poses, all apparently speaking. The band reads: ASCENDENS XPS IN ALTUM CAPTIVAM DUXIT CAPTIVITATE / MICAEL ARCANGELUS PUGNAVIT CUM DRACONE ("Ascending on high, Christ led the captive from captivity / Michael the Archangel fought with the dragon").