Siege Perilous
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.
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 Siege Perilous is so strictly reserved that it is fatal to anyone else who sits in it. Another version of this story is related in Alfred, Lord Tennyson's Idylls of the King.