And when he awoke, and looked round him, it seemed to him that he was enclosed in the strongest tower in the world, and laid upon a fair bed.  Then said he to the dame:  “My lady, you have deceived me, unless you abide with me, for no one hath power to unmake this tower but you alone.”  She then promised she would be often there, and in this she held her covenant with him.  And Merlin never went out of that tower where his Mistress Viviane had enclosed him; but she entered and went out again when she listed.

After this event Merlin was never more known to hold converse with any mortal but Viviane, except on one occasion.  Arthur, having for some time missed him from his court, sent several of his knights in search of him, and, among the number, Sir Gawain, who met with a very unpleasant adventure while engaged in this quest.  Happening to pass a damsel on his road, and neglecting to salute her, she revenged herself for his incivility by transforming him into a hideous dwarf.  He was bewailing aloud his evil fortune as he went through the forest of Breceliande, when suddenly he heard the voice of one groaning on his right hand; and, looking that way, he could see nothing save a kind of smoke, which seemed like air, and through which he could not pass.  Merlin then addressed him from out the smoke, and told him by what misadventure he was imprisoned there.  “Ah, sir!” he added, “you will never see me more, and that grieves me, but I cannot remedy it; I shall never more speak to you, nor to any other person, save only my mistress.  But do thou hasten to King Arthur, and charge him from me to undertake, without delay, the quest of the Sacred Graal.  The knight is already born, and has received knighthood at his hands, who is destined to accomplish this quest.”  And after this he comforted Gawain under his transformation, assuring him that he should speedily be disenchanted; and he predicted to him that he should find the king at Carduel, in Wales, on his return, and that all the other knights who had been on like quest would arrive there the same day as himself.  And all this came to pass as Merlin had said.

Merlin is frequently introduced in the tales of chivalry, but it is chiefly on great occasions, and at a period subsequent to his death, or magical disappearance.  In the romantic poems of Italy, and in Spenser, Merlin is chiefly represented as a magical artist.  Spenser represents him as the artificer of the impenetrable shield and other armor of Prince Arthur ("Faery Queene,” Book I., Canto vii.), and of a mirror, in which a damsel viewed her lover’s shade.  The Fountain of Love, in the “Orlando Innamorata,” is described as his work; and in the poem of “Ariosto” we are told of a hall adorned with prophetic paintings, which demons had executed in a single night, under the direction of Merlin.

The following legend is from Spenser’s “Faery Queene,” Book iii., Canto iii.: 

Caer-Merdin, or CAERMARTHEN (in Wales), Merlin’s tower, and the imprisoned fiends.