In Arthurian legend, the Siege Perilous (also known as The Perilous Seat) 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. This knight is either Percival or Sir Galahad, depending on the version of the story. The Siege Perilous is so strictly reserved that it is fatal to anyone else who sits in it.
In Thomas Malory's Le Morte D'Arthur, in an account taken from the Vulgate Queste del Saint Graal, the newly knighted Sir Galahad takes the seat in Camelot on Whitsunday, 454 years after the death of Jesus. The tale itself appears in the Didot Perceval, where Perceval occupies the seat, and according to some scholars, can be further traced to Celtic mythology involving a kingship ritual that has parallels in the Irish Lia Fail.
- Malory T., Morte Darthur, The Globe Edition, Macmillan and Co., London 1868, Book XI, p.326: "he shall be born that shall sit there in that siege perilous, and he shall win the Sangreal." Facsimile by Google Books
- Norris, Ralph C. Malory's Library: The Sources of the Morte Darthur (D.S. Brewer, 2008), p. 114.
- R.S. Loomis. Celtic Myth and Arthurian Romance (Academy Chicago Publishers; revised ed. 1997).
- Tennyson, A., Idylls of the King, 1856: "And Merlin called it 'The Siege perilous'"(forgottenbooks.org 2007 edition at Google Books)