Nightbringer | The Arthurian Online Encyclopedia

Morgan’s Drinking Horn

This magical drinking horn, “harnessed with gold”, could only be used in safety by ladies who were true to their husbands. If the drinker were false to her husband, all the drink would spill. Morgan le Fay (who could not herself have honestly drunk from it) sent this horn to Arthur in another attempt to publicize Guenevere’s unfaithfulness, but Sir Lamorak stopped the messenger and made him take it to King Mark instead.

Of a hundred ladies in Mark’s court, including La Beale Isoud (Isolde), only four could drink cleanly. To the credit of the men, when the angered King Mark swore to burn Isoud and the other shamed ladies,

[t]hen the barons gathered them together, and said plainly they would not have those ladies burnt for an horn made by sorcery, that came from a false a sorceress and witch as then was living. For that horn did never good, but caused strife and debate, and always in her days she had been an enemy to all true lovers. So there were many knights made their avow, an ever they met with Morgan le Fay, that they would show her short courtesy.