The magnificent Royal Pantheon lies beneath the chancel. It contains the mortal remains of all the Spanish monarchs from the time of Carlos V, with the exception of Felipe V, Ferdinand VI and Amadeus of Savoy. The octagonal chapel was built between 1617 and 1654 according to drawings by J. Bautista Crescenzi. The altar is made out of jasper and the 26 sarcophagi from marble and bronze. The 19C Panteón de los Infantes includes the queens whose children did not succeed to the throne, as well as the children.