As King Arthur and his knights assembled at Camelot all at once they heard a great crack of thunder. Then, in the middle of the blast a glorious sunbeam entered the room, and all the men were touched by the grace of the Holy Ghost.

Then there entered into the hall the Holy Grail covered with white samite, but there was none might see it nor who bare it. And there was all the hall full filled with good odours... and when the Holy Grail had been borne through the hall, then the holy vessel departed, suddenly, that they wist not where it became.
- Malory.

King Arthur stood up and offered thanks to God for such a miracle, and then Sir Gawaine arose and said,

I will make here avow, that to-morrow, without longer abiding, I shall labour in the quest of the Sangreal, that I shall hold me out a twelve-month and a day, or more if need be, and never shall I return again unto the court till I have seen it more openly than it hath been seen here
- Malory.

And then all the knights of the Round Table arose and vowed the same: To seek the Holy Grail.