The completion of the Arthurian theme was the prose novel by the Englishman Thomas Malory (circa 1417-1471) "The Death of Arthur", which is at the same time a translation of the novel compiled at the turn of the 13th and 14th centuries. collection of French prose novels about Arthur, and the original development of the plot. In this book, the events of Arthur's biography are somewhat changed and shifted. The campaign against Rome takes place at the beginning of the reign of Arthur and is successful. An attempt to seize the throne and the queen (she does not want to marry Modred) is made because Arthur's army is at war with Lancelot, who is accused of having an affair with Guinevere, and many knights have already died in the fight against him. Thus, the reason for the death of the kingdom of Arthur is a split among the knights of the Round Table, and Modred's betrayal is only the last push.
Back in the 20th century Arthur becomes the most popular hero in Europe. Around 1190 Arthur's tomb is allegedly found at Glastonbury Abbey. In 1312, the poet Jean de Longillon in his poem "The Pledge of the Peacock" lists the nine best warriors of all times and peoples. These are three pagan knights - Hector, Alexander the Great and Julius Caesar; three Jews - Joshua, King David and Judas Maccabee; three Christian ones - King Arthur, Charlemagne and the conqueror of Jerusalem, Gottfried of Bouillon. In the XV century. one of the French courtiers seriously claims that the failures of England in the Hundred Years War are explained by the fact that the best knights of this country once fell with King Arthur.
Simultaneously with the development of Arthur's biography, another development of this theme takes place in the novels: independent works appear about certain knights of the Round Table, about their exploits. In the XIII century. In the book of Robert de Boron "The Romance of the Grail" the theme of the Grail is recorded for the first time - the cup from which Christ drank during the Last Supper and into which Joseph of Arimathea collected His blood. At the same time, the Grail is a magical all-saturating cauldron of Celtic myths, and in Wolfram von Eschenbach's novel "Parzival" (circa 1210) - a kind of magic stone. The Grail is adjacent to the spear of the centurion Longinus, which completed the torment of Christ on the cross, but at the same time it is a magical weapon of Celtic myths that heals the wounds inflicted by it. These sacred relics are kept in the enchanted castle of Monsalvas, and only a perfect knight can acquire them, so the search for the Grail is the search for spiritual perfection.