Heraldry on the first page of the Psalms text strongly suggests that this Psalter was commissioned by King Edward I for the marriage of his son Alphonso, to Margaret, daughter of Florent V, Count of Holland, which was to take place in 1284. Alphonso died before the wedding, however, and the decoration of the manuscript was left incomplete. Additions were made in the early 14th century, probably before 1316. In the lower border a horse lies dying, presumably wounded by the griffin (a fabulous monster with the head, wings, and claws of an eagle, and the hindquarters of a lion) which is being speared by the horse's rider, a soldier in a full suit of chain-mail.