A famous painting [at left] by the important British pre-Raphaelite artist Cowper [1877-1958] depicts Lancelot asleep as four British Isles queens espy him. This scene comes from the many stories of the round table, collected in a volume by Howard Pyle here in 1905. There are other paintings of the same scene, ie. one by another British painter, Calderon [1833-1898] from 1908. Be sure to know his famous piece "St. Elizabeth of Hungary's Great Act of Renunciation" (1891).
Here's an excerpt from the tales of King Arthur, read more here:
How Sir Launcelot was Found in a Sleep by Queen Morgana le Fay, and Three Other Queens who were with Her, and How He was Taken to a Castle of Queen Morgana's and of What Befell Him There.
So Sir Launcelot lay in deep slumber under that apple-tree, and knew neither that Sir Lionel had left him nor what ill-fortune had befallen that good knight. Whilst he lay there sleeping in that wise there came by, along the road, and at a little distance from him, a very fair procession of lordly people, making a noble parade upon the highway.
The chiefest of this company were four ladies, who were four queens. With them rode four knights, and, because the day was warm, the four knights bore a canopy of green silk by the four corners upon the points of their lances in such wise as to shelter those queens from the strong heat of the sun.
And those four knights rode all armed cap-a-pie on four noble war-horses, and the four queens, bedight in great estate, rode on four white mules richly caparisoned with furniture of divers colors embroidered with gold.
After these lordly folk there followed a very excellent court of esquires and demoiselles to the number of a score or more; some riding upon horses and some upon mules that ambled very easily.
Now all these folk of greater or lesser degree were entirely unaware that Sir Launcelot lay sleeping so nigh to them as they rode by chattering very gayly together in the spring-time weather, taking great pleasure in the warm air, and in growing things, and the green fields, and the bright sky; and they would have had no knowledge that the knight was there, had not Sir Launcelot's horse neighed very lustily.
Thereupon, they were aware of the horse, and then they were aware of Sir Launcelot where he lay asleep under the apple-tree, with his head lying upon his helmet.
Now foremost of all those queens was Queen Morgana le Fay (who was King Arthur's sister, and a potent, wicked enchantress, of whom much hath been told in the Book of King Arthur), and besides Queen Morgana there was the Queen of North Wales, and the Queen of Eastland, and the Queen of the Outer Isles.
Now when this party of queens, knights, esquires, and ladies heard the war-horse neigh, and when they beheld Sir Launcelot where he lay, they drew rein and marvelled very greatly to see a knight sleeping so soundly at that place, maugre all the noise and tumult of their passing. So Queen Morgana called to her one of the esquires who followed after them, and she said to him: "Go softly and see if thou knowest who is yonder knight; but do not wake him."
So the esquire did as she commanded; he went unto that apple-tree and he looked into Sir Launcelot's face, and by hap he knew who it was because he had been to Camelot erstwhiles and he had seen Sir Launcelot at that place.
So he hastened back to Queen Morgana and he said to her: "Lady, I believe that yonder knight is none other than the great Sir Launcelot of the Lake, concerning whom there is now such report; for he is reputed to be the most powerful of all the knights of King Arthur's Round Table, and the greatest knight in the world, so that King Arthur loves him and favors him above all other knights."
Now when Queen Morgana le Fay was aware that the knight who was asleep there was Sir Launcelot, it immediately entered her mind for to lay some powerful, malignant enchantment upon him to despite King Arthur. For she too knew how dear Sir Launcelot was to King Arthur, and so she had a mind to do him mischief for King Arthur's sake.
So she went softly to where Sir Launcelot lay with intent to work some such spell upon him. But when she had come to Sir Launcelot she was aware that this purpose of mischief was not possible whilst he wore that ring upon his finger which the Lady of the Lake had given him; wherefore she had to put by her evil design for a while.
But though she was unable to work any malign spell upon him, she was
able to cause it by her magic that that sleep in which he lay should remain unbroken for three or four hours. So she made certain movements of her hands above his face and by that means she wove the threads of his slumber so closely together that he could not break through them to awake.
After she had done this she called to her several of the esquires who were of her party, and these at her command fetched the shield of Sir Launcelot and laid him upon it. Then they lifted him and bore him away, carrying him in that manner to a certain castle in the forest that was no great distance away. And the name of that castle was Chateaubras and it was one of Queen Morgana's castles.
And all that while Sir Launcelot wist nothing, but lay in a profound sleep, so that when he awoke and looked about him he was so greatly astonished that he knew not whether
he was in a vision or whether he was awake. For whilst he had gone asleep beneath that apple-tree, here he now lay in a fair chamber upon a couch spread with a coverlet of flame-colored linen.