As Sir Mordred was at Dover with his host, there came King Arthur with a great navy of ships, galleys, and carracks. And there was Sir Mordred ready awaiting upon his landage, to keep his own uncle from landing in the country that he was king over. Then there was launching of great boats and small, full of noble men of arms, and there was much slaughter of gentle knights, and many a bold baron was laid full low on both sides. But King Arthur was so courageous that there might no manner of knights prevent him from landing, and his knights fiercely followed him.
So they landed in spite of Sir Mordred and all his power, and they put him aback, so that he fled and all his people. When this battle was done, King Arthur let bury his dead, and then was the noble knight Sir Gawaine found in a great boat lying more than half dead. When Sir Arthur wist that Sir Gawaine was laid so low, he went unto him and made sorrow out of measure, for this sister's son was the man in the world that he most loved. Sir Gawaine felt that he must die, for he was smitten upon the old wound that Sir Launcelot had given him afore the city of Benwick. He now knew that he was the cause of this unhappy war, for had Sir Launcelot remained with the King, it would never have been, and now King Arthur would sore miss his brave knights of the Round Table.
Then he prayed his uncle that he might have paper, pen, and ink, and when they were brought, he with his own hand wrote thus, as the French book maketh mention: "Unto Sir Launcelot, flower of all noble knights that ever I heard of, or saw by my days, I, Sir Gawaine, King Lot's son of Orkney, sister's son unto the noble King Arthur, send thee greeting, and let thee have knowledge, that this tenth day of May, through the same wound that thou gavest me I am come to my death. And I will that all the world wit that I, Sir Gawaine, knight of the Table Round, sought my death; it came not through thy deserving, but it was mine own seeking. Wherefore I beseech thee, Sir Launcelot, to return again unto this realm, and see my tomb, and pray some prayer, more or less, for my soul. For all the love that ever was betwixt us, make no tarrying, but come over the sea in all haste, that thou mayest with thy noble knights rescue that noble king that made thee knight, that is my lord Arthur, for he is full straitly bestead with a false traitor, my half-brother, Sir Mordred. We all landed upon him and his host at Dover, and there put him to flight, and there it misfortuned me to be stricken in the same wound the which I had of thy hand, Sir Launcelot. Of a nobler man might I not be slain. This letter was written but two hours and an half afore my death, with mine own hand, and so subscribed with part of my heart's blood."
Then Sir Gawaine wept, and King Arthur wept, and then they swooned both. When they awaked both, the King made Sir Gawaine to receive the sacrament, and then Sir Gawaine prayed the King to send for Sir Launcelot, and to cherish him above all other knights. And so at the hour of noon, Sir Gawaine yielded up the spirit, and the King let inter him in a chapel within Dover Castle.
Then was it told King Arthur that Sir Mordred had pitched a new field upon Barham Down. Upon the morn the King rode thither to him, and there was a great battle betwixt them, and much people were slain on both parties. But at the last Sir Arthur's party stood best, and Sir Mordred and his party fled to Canterbury. Upon this much people drew unto King Arthur, and he went with his host down by the seaside, westward towards Salisbury, and there was a day assigned between him and Sir Mordred when they should meet in battle upon a down beside Salisbury, not far from the sea.
In the night before the battle King Arthur dreamed a wonderful dream, and it seemed to him verily that there came Sir Gawaine unto him, and said; "God giveth me leave to come hither for to warn you that, if ye fight to-morn with Sir Mordred, as ye both have assigned, doubt ye not ye must be slain, and the most part of your people on both parties. For the great grace and goodness that Almighty Jesu hath unto you, and for pity of you and many other good men that there shall be slain, God hath sent me to you, of His special grace, to give you warning, that in no wise ye do battle to-morn, but that ye take a treaty for a month; and proffer ye largely, so as to-morn to be put in delay, for within a month shall come Sir Launcelot, with all his noble knights, and rescue you honourably, and slay Sir Mordred and all that ever will hold with him."
Then Sir Gawaine vanished, and anon the King commanded Sir Lucan and his brother, Sir Bedivere, with two bishops with them, and charged them to take a treaty for a month with Sir Mordred in any wise they might. So then they departed, and came to Sir Mordred, where he had a grim host of an hundred thousand men. There they entreated Sir Mordred long time, and at the last he was agreed to have Cornwall and Kent by King Arthur's days, and after the days of King Arthur all England.