Alas, me sore repenteth, said the king, that ever Sir Launcelot should be against me. Now I am sure the noble fellowship of the Round Table is broken for ever, for with him will many a noble knight hold; and now it is fallen so, said the king, that I may not with my worship, but the queen must suffer the death. So then there was made great ordinance in this heat, that the queen must be judged to the death. And the law was such in those days that whatsomever they were, of what estate or degree, if they were found guilty of treason, there should be none other remedy but death; and outher the men or the taking with the deed should be causer of their hasty judgment. And right so was it ordained for Queen Guenever, because Sir Mordred was escaped sore wounded, and the death of thirteen knights of the Round Table. These proofs and experiences caused King Arthur to command the queen to the fire there to be brent.
Thomas Malory’s Morte d’Arthure