Siege Perilous

In Arthurian legend, the Siege Perilous (Welsh: Gwarchae Peryglus, also known as The Perilous Seat, Welsh: Sedd Peryglus) is a vacant seat at the Round Table reserved by Merlin for the knight who would one day be successful in the quest for the Holy Grail.

[2] In Thomas Malory's 1485 book Le Morte d'Arthur, in an account taken from the Vulgate Cycle Queste del Saint Graal,[3] the newly knighted Sir Galahad takes the seat in Camelot on Whitsunday, 454 years after the death of Jesus.

[4] Originally, this motif about the seat and the grail belonged to Perceval, but the Lancelot-Grail Cycle transferred it to the new Cistercian-based hero Galahad.

[5][self-published source] According to many scholars, the motif of the dangerous seat can be further traced to Welsh, Cornish, and Breton mythology, from which the bulk of the Arthurian legend was derived.

According to this theory, the Siege Perilous was a half-remembered version of a Celtic kingship ritual that has parallels in the Irish Lia Fáil.