Colombe appears in the Arthurian legend during the tale of Sir Balin, the knight who would become known as the Knight of the Two Swords. The story begins at Camelot, where a damsel arrives bearing a sword that can be drawn only by a knight who is pure and without villainy. Many try and fail, but Balin, who has been imprisoned for killing a cousin of the king, draws the weapon with ease. The Lady of the Lake, the enchantress who gave Arthur his sword Excalibur, demands that Balin surrender the sword to her, but he refuses, for he recognises her as the murderer of his mother. In the quarrel that follows, Balin beheads the Lady of the Lake's messenger before the whole court. King Arthur is furious, and Sir Lanceor, an Irish knight of great pride, rides out from Camelot to bring Balin back in chains or to kill him for the insult to the king.

Colombe was Lanceor's paramour, the woman who loved him above all others. When Lanceor rode from Camelot in pursuit of Balin, she mounted a fair palfrey and rode after him at full speed, her heart already heavy with a fear she could not name. She reached the heath where the two knights had met, but she was too late. Balin had already struck the fatal blow, and Lanceor lay dead upon the ground, his blood soaking into the earth. Colombe dismounted and went to him, kneeling beside his body and weeping with a grief that had no bottom. Then, in an act of desolation that would make her name immortal in the legend, she took Lanceor's own sword, placed the point against her breast, and fell upon it. The blade pierced her heart, and she died across the body of the man she loved, her blood mingling with his upon the grass.

King Mark of Cornwall, who happened to be travelling in those parts, came upon the scene and was moved to pity. He ordered his men to dig a grave, and he buried Lanceor and Colombe together in a single tomb upon the heath. Over their grave he raised a stone and inscribed upon it the story of their love and their death. But the tomb was not to rest in peace. Merlin, the wizard and seer who served King Arthur, arrived and defaced the inscription that King Mark had carved. In its place, Merlin wrote a prophecy: that the two greatest knights in all the world, Sir Launcelot du Lake and Sir Tristram of Lyonesse, would one day fight a great battle upon that very ground. Merlin added another prophecy as well, foretelling that Balin would one day strike the Dolorous Stroke, a blow so terrible that it would wound the truest knight alive and lay three kingdoms waste for twelve years.

Colombe's story is brief, spanning no more than a few pages in Malory's great book, but it resonates through the whole of the Arthurian legend. Her death sets a pattern of lovers who cannot survive separation that would be repeated in the tales of Tristram and Isolde, of Lancelot and Guinevere, and of Elaine of Astolat. The tomb that King Mark built and Merlin defaced became a sacred site in the landscape of Arthurian Britain, a place where love and prophecy met upon a heath near Camelot. In later retellings, the tomb is said to have stood until the fall of the Round Table itself, when the wars between Launcelot and Arthur made Merlin's prophecy come true in ways that no one at Camelot could have foreseen.