One of the most outstanding features of the Cathedral is the Baroque altarpiece called El Transparente. Its name refers to the unique illumination provided by a large skylight cut very high up into the thick wall across the ambulatory behind the high altar, and another hole cut into the back of the altarpiece itself to allow shafts of sunlight to strike the tabernacle. This lower hole also allows persons in the ambulatory to see through the altarpiece to the tabernacle, so that they are seeing though its transparency, so to speak. The work was commissioned by Diego de Astorga y Céspedes, Archbishop of Toledo, who wished to mark the presence of the Holy Sacrament with a glorious monument. El Transparente is several storeys high and is extraordinarily well-executed with fantastic figures done in stucco, painting, bronze castings, and multiple colors of marble; it is a masterpiece of Baroque mixed media by Narciso Tomé and his four sons (two architects, one painter and one sculptor). The illumination is enhanced when the Mass is being said in the mornings and the sun shines from the east, shafts of sunlight from the appropriately oriented skylight striking the tabernacle through the hole in the back of the retable, giving the impression that the whole altar is rising to heaven.