The Pyx Chamber formed the undercroft of the monks' dormitory. It dates to the late 11th century and was used as a monastic and royal treasury. The outer walls and circular piers are of 11th-century date, several of the capitals were enriched in the 12th century and the stone altar added in the 13th century. The term pyx refers to the boxwood chest in which coins were held and presented to a jury during the Trial of the Pyx, in which newly minted coins were presented to ensure they conformed to the required standards.