These knights were well known to Arthur and were his friends; but like Guinevere they had not known him, because he kept down the visor of his helmet when he did battle with them. And they returned and told Guinevere that they were conquered by an unknown knight who had ordered them to come to her and do her bidding.
Guinevere was guarded in the castle of Cameliard by a knight named Sir Mordaunt of North Umber who was greatly desirous of wedding her. And at last he kept her a close prisoner and with six companions mounted guard before the castle proclaiming that unless some champions came forward in her behalf he would marry her against her will.
At this Guinevere was greatly distressed, for she had grown to love the unknown knight that she had seen in the garden, and she asked the four that were in her charge to go forth and do battle with the knights that guarded her. But they would not, although they were bound to do her word, because they were angered that she should demand this of them when she knew that they were only four against seven. When Arthur returned, however, he placed himself at their head and they charged the seven knights so fiercely that three were slain in their onslaught and the others fled. And shortly after this Guinevere was brought to Arthur for marriage, and he disclosed his state as King, and their nuptials were celebrated with gorgeous pomp and ceremony.
Merlin told Arthur to ask from Guinevere's father, whose name was Leodegrance and who was himself a king, a marvelous round table that he possessed. This table had magic powers, said Merlin, and Arthur would add greatly to the strength of his kingdom by possessing it. The table had many marvelous properties,—and the chairs that went with it were equally marvelous. The names of those who should sit in them appeared in letters of gold when such knights approached, and disappeared again when they rose to depart. There was also a seat richer than the rest for the King himself—and another chair, wonderfully carven and wrought with gems, that was called the "Seat Perilous," where even Arthur might not sit—for that chair was reserved for the knight who should look upon the "Holy Grail," a vessel containing the blood of Christ that had been taken to Heaven on his death. It could only be beheld by the purest knight that went in quest of it, which Arthur could not do, because he must rule his kingdom.
Then Arthur gathered all the best knights in the realm about him and they were called "the Knights of the Round Table" and they bound themselves by vows to noble deeds and gallant conduct, to redress wrongs, to think no evil or allow it to appear in any guise at the Round Table. And through the deeds of his knights of the Round Table Arthur's name became even greater in his kingdom than it had ever been before.
But little by little doubt and suspicion began to appear among Arthur's knights, and these were fostered by the evil plots of Arthur's nephew, Modred. Above all, Modred hated a knight named Sir Lancelot, who, with the exception of the King, was the bravest knight in Britain. Sir Lancelot was loved by Queen Guinevere, and loved her in return. And through Modred's schemes it befell that fighting commenced between Lancelot and other knights of the Round Table, in which many were slain. And then the whole kingdom of Britain was torn apart and Arthur's former glory was lost; and at last the unhappy King even found himself at war with his former friend, Sir Lancelot himself, who had stolen the love of the Queen.
After bitter fighting Sir Lancelot went back to his own country of Brittany, taking Queen Guinevere with him, beyond the sea, and Arthur pursued him there. And while Arthur was laying siege to Sir Lancelot's castle, the false knight Modred rose against Arthur in his own country, hatching a rebellion against the King, so Arthur had to give up the siege of Lancelot's castle and return to Britain to fight against the traitors that had risen from the ranks of his own subjects.
This was the last war that Arthur ever engaged in. Merlin had foretold that when the seats at the Round Table had all been filled, Arthur's kingdom must gradually decline. The seats had been filled long since, and the decline had come about through the distrust and the evil deeds of Arthur's own knights. And now he must fight a number of them both in the ranks of Lancelot and under the banner of Modred.
In a battle with Modred's forces King Arthur's army fought so fiercely that when dusk fell almost all the men on both sides who had engaged in that fight were slain, and none were left but the leaders of the opposing forces. And Arthur engaged in personal combat with Modred just as the sun was going down. Now Arthur had long since lost the scabbard of his sword, Excalibur, so it was possible to wound or slay him in battle, although he that stood up against the stroke of that sword must also be slain. And this very thing came to pass in Arthur's battle with Modred. For as Arthur ran him through, Modred struck him so terrible a blow on the head that his helmet was cut in two and the sword sank deep in his skull.
Grievously wounded, Arthur was carried from the field by one of his few remaining knights, named Sir Bedivere; and Arthur, seeing that he must die, gave to Sir Bedivere the sword, Excalibur, telling him to throw it in the lake.