The single manuscript in which the Morte survives was a well-circulated text; whereas the Gawain manuscript has uncertain circulation issues, the Morte manuscript is known to have existed with a wider publication, even if only a single one now survives; the Thornton manuscript is the name of this text and it dates from the 15th century which contains many stories.
The copy of the Morte text which is included in the Thornton manuscript was likely composed at the end of the 14th century. The story is that after Arthur conquers the known world, he degenerates into a war-leader who conquers merely because he now can. The author is pro-Arthur but very critical of the Arthurian tradition.
Mordred is treated sympathetically though he is a villain. Guinevere is fertile instead of sterile and is able to conceive a baby. Arthur has several prophetic dreams, has two swords—Excalibur and Clarent, the latter of which seems to function as a sword of peace. Genre wise the poem is unstable and veers between Romances, history, and tragedy and epic and even the “Mirror for Princes” tradition, which instructs princelings on proper behavior.
The introductory section of the Morte text is lifted from Monmouth, along with most of the basic plot, but the description is overhauled. Indeed, many of the scenes become much more dramatic and a rhetorical flair and asks the readers to puzzle out its meaning. The text is more graphic and bloody with lengthy descriptions of battle. The poet pushes King Arthur as a hero who faces down the corrupted king of Rome who is allied with monsters and heathens. After his victory over Rome, Arthur decides to continue conquering territories and serves as a shift in the “Mirrors for Princes” pedagogy in how Arthur rules as a king; Arthur transitions from a just to an unjust king.
In the narrative, Arthur has a second dream in which the fortune wheel reminds him of his fallibility via a beautiful woman in the wood who drops him in the mud. So, Mordred betrayals Arthur and conceives a child with Guinevere. Arthur, of course, returns to his home to confront Mordred with Arthur’s sword Clarent. As with the typical ending narrative, Arthur is killed but is not taken to Avalon to heal, but rather dies after he orders Mordred off-springs be killed. A bleak conclusion.