We’ve all heard stories about King Arthur of Camelot, who according to medieval legend led British forces (including his trusted Knights of the Round Table) in battle against Saxon invaders in the early sixth century. But was King Arthur actually a real person, or simply a hero of Celtic mythology?

Though debate has gone on for centuries, historians have been unable to confirm that Arthur really existed. He doesn’t appear in the only surviving contemporary source about the Saxon invasion, in which the Celtic monk Gildas wrote of a real-life battle at Mons Badonicus (Badon Hills) around 500 A.D. Several hundred years later, Arthur appears for the first time in the writings of a Welsh historian named Nennius, who gave a list of 12 battles the warrior king supposedly fought. All drawn from Welsh poetry, the battles took place in so many different times and places that it would have been impossible for one man to have participated in all of them.

Later Welsh writers drew on Nennius’ work, and Arthur’s fame spread beyond Wales and the Celtic world, particularly after the Norman conquest of 1066 connected England to northern France. In the popular 12th-century book History of the Kings of Britain, Geoffrey of Monmouth wrote the first life story of Arthur, describing his magic sword Caliburn (later known as Excalibur), his trusted knight Lancelot, Queen Guinevere and the wizard Merlin. An irresistible blend of myth and fact, the book was supposedly based on a lost Celtic manuscript that only Geoffrey was able to examine.

A series of romances by the French poet Chrétien de Troyes gave Arthur’s quest a spiritual motive by introducing his search for the mysterious Holy Grail. Though Arthur may not have been a real person, his mythic power would only grow stronger as the centuries passed. English rulers from Henry VIII to Queen Victoria have appropriated the Arthur legend for political purposes, while countless writers, painters, photographers, filmmakers and other artists have produced their own versions for posterity.