A large number of Arthurian stories exist, attesting to the popularity of the Arthurian legend. These are all fictionalized tales: they cannot tell us verifiable facts about specific historical events. However, evolution of the tales does give us hints about the evolution of social life in medieval Europe.
In the earliest sources, King Arthur is the central figure and primarily esteemed as a courageous warrior and empire builder. He exults in a sometimes bloodthirsty way in killing enemies and is not the courtly figure he will later become. What this shows us, as does the epic poem Beowulf, is the central importance of the warrior to early medieval society. In a period of breakdown as the Roman empire collapsed and stopped providing protection to former outposts, societies depended on a fierce leader who could rally other soldiers around him and defend territories that otherwise would have fallen into chaos and anarchy. The valorization of Arthur as empire builder also reveals early medieval nostalgia for a return to the Roman empire.
By the time of the highly influential twelfth-century work History of the Kings of Britain by Geoffrey of Monmouth, Arthur has begun his evolution into the courtly figure he will become. In a famous quote, we learn that he
invited over to him all persons whatsoever that were famous for valour in foreign nations [and] he began to augment the number of his domestics, and introduced such politeness into his court, as people of the remotest countries thought worthy of their imitation. So that there was not a nobleman who thought himself of any consideration, unless his clothes and arms were made in the same fashion as those of Arthur's knights.
The above quote shows that by the 1100s, although warriors were still highly valued, European society had stabilized and acquired enough excess resources to allow it to concentrate on developing a refined social order. Manners, clothing, and fashion have a new importance as wealth and stability have increased.
By the time of Thomas Malory's late fifteenth- century Le Morte D'Arthur, the stories had evolved to put more emphasis on the figures around Arthur and more emphasis on tales of love and individual acts of valor rather than fighting battles. Arthur, now sometimes pictured as indolent and out of touch, could be used to critique the current monarchy, showing the continuing undermining of authority even a century after the high point of the Black Death.
Taken as a whole, the legends move from depicting a culture in breakdown depending on a strong and sometimes barbaric warrior leader to survive to a flattering picture of a wealthy, well mannered, and comfortable noble elite.