knights were to fall, according to the legend, in one great battle.
Modred, the king's nephew, had been left in charge of the kingdom during
Arthur's absence, and had betrayed him and tried to dethrone him, meaning
to crown himself king. Many people joined with him, saying that under
Arthur they had had only war and fighting, but under Modred they would
have peace and bliss. Yet nothing was farther from Modred's purpose than
bliss or peace, and it was agreed at last that a great battle should be
fought for the kingdom.

On the night of Trinity Sunday, King Arthur had a dream. He thought he
sat in a chair, upon a scaffold, and the chair was fastened to a wheel. He
was dressed in the richest cloth of gold that could be made, but far
beneath him he saw a pit, full of black water, in which were all manner of
serpents and floating beasts. Then the wheel began to turn, and he went
down, down among the floating things, and they wreathed themselves about
him till he cried, "Help! help!"

Then his knights and squires and yeomen aroused him, but he slumbered
again, not sleeping nor thoroughly waking. Then he thought he saw his
nephew, Sir Gawaine, with a number of fair ladies, and when King Arthur
saw him, he said, "O fair nephew, what are these ladies who come with
you?" "Sir," said Sir Gawaine, "these are the ladies for whose protection
I fought while I was a living man, and God has given them grace that they
should bring me thither to you, to warn you of your death. If you fight
with Sir Modred to-morrow, you must be slain, and most of your people on
both sides." So Sir Gawaine and all the ladies vanished, and then the king
called upon his knights and squires and yeomen, and summoned his lords and
bishops. They agreed to propose to Sir Modred that they should have a
month's delay, and meanwhile agreed to meet him with fourteen persons on
each side, besides Arthur and Modred.