Report by Mary Alexander on a piece of green porphyry recovered from a securely dated mid-late 13th century layer during excavation by the Guildford Group of the SyAS, in 1981. Porphyry is only known from two medieval contexts in England: Westminster Abbey and Canterbury Cathedral. This piece must be a discard from work being carried out at the castle, possibly associated with a chapel known to have been constructed in 1268 for Eleanor of Castile. (291)