Legend:
King Arthur was a legendary British leader who, according to medieval histories and romances, led the defence of Britain against Saxon invaders in the late 5th and early 6th centuries.
Uther Pendragon, also known as King Uther, is a legendary king of sub-Roman Britain and the father of King Arthur.
Uther’s family is based on some historical figures; Aurelius Ambrosius is Ambrosius Aurelianus, mentioned by Gildas, though his connection to Constantine and Constans is unrecorded. It is possible that Uther himself is based at least partially on Tewdrig, a historical king of Glywysing in the sixth century, given the strong similarities between their death stories. Depending on the source, Uther may either be the son of Constantine III, as is related in the Welsh Triad 51, or he may be the son of Constantine of Dumnonia, as related in Monmouth’s History of the Kings of Britain.
Reality:
Flavius Claudius Constantinus, known in English as Constantine III, was a Roman general who declared himself Western Roman Emperor in Britannia in 407 and established himself in Gaul. He was co-emperor from 409 until 411.
Riothamus was a Romano-British military leader, who was active circa AD 470. He fought against the Goths in alliance with the declining Western Roman Empire. He is called “King of the Britons” by the 6th-century historian Jordanes, but the extent of his realm is unclear.
Riothamus has been identified as a candidate for the historical King Arthur by several scholars over the centuries, notably the historian Geoffrey Ashe, primarily due to Riothamus’s activities in Gaul, which bear a casual resemblance to King Arthur’s Gallic campaign as first recorded by Geoffrey of Monmouth in his Historia Regum Britanniae. Geoffrey Ashe has suggested a link between Riothamus’ alleged betrayal by Arvandus and Arthur’s betrayal by Mordred in the Historia Regum Britanniae, and proposes that Riothamus’ last known position was near the Burgundian town of Avallon (not noted by any ancient source mentioning Riothamus), which he suggests is the basis for the Arthurian connection to Avalon.
After:
The Kingdom of England came into being in 927 under Aethelstan. He was king of Wessex and was recognized as king by the Mercian. He conquered the Viking kingdom of York making him the first Anglo Saxon king of the whole of England.
Else:
One theory suggests that Lucius Artorius Castus, a Roman military commander who served in Britain in the late 2nd century or early 3rd century, was a prototype of Arthur. Artorius is known from two inscriptions that give details about his service. After a long career as a centurion in the Roman army, he was promoted to prefect of Legio VI Victrix, a legion headquartered in Eboracum (present-day York, England). He later commanded two British legions on an expedition against either the Armoricans (in present-day Brittany) or the Armenians. He subsequently became civilian governor of Liburnia in modern Croatia, where he died.
Kemp Malone first made the connection between Artorius and King Arthur in 1924. Noting that the Welsh name Arthur plausibly derives from the Latin Artorius, Malone suggested that certain details of Castus’ biography, in particular his possible campaign in Brittany and the fact that he was obliged to retire from the military (perhaps because of an injury), may have inspired elements of Geoffrey of Monmouth’s depiction of King Arthur. Later scholars have challenged the idea, based on the fact that Artorius lived two to three centuries before the period typically associated with Arthur, and the fact that the parts of the inscriptions ostensibly similar to Arthur’s story are open to interpretation.
Malone’s idea attracted little attention for decades, but it was revived in the 1970s as part of a theory known as the “Sarmatian connection”. In a 1975 essay, Helmut Nickel suggested that Artorius was the original Arthur, and that a group of Sarmatian cavalry serving under him in Britain inspired the Knights of the Round Table. Nickel wrote that Castus’ Sarmatian unit fought under a red dragon banner and that their descendants were still in Britain in the 5th century; he also identified similarities between the Arthurian legend and traditions associated with the Sarmatians and other peoples of the Caucasus region. He suggested that the Sarmatians’ descendants kept Castus’ legacy alive over the centuries and mixed it with their ancestral myths involving magical cauldrons and swords.
Independently of Nickel, C. Scott Littleton developed a more elaborate version of the Sarmatian connection. Littleton first wrote about the theory with Anne C. Thomas in 1978, and expanded on it in a 1994 book co-authored by Linda Malcor, From Scythia to Camelot. Littleton and Malcor argued that Artorius and the Sarmatian cavalry were the inspiration for King Arthur and his knights, but that many elements of Arthur’s story derive from Caucasian mythology, ostensibly brought to Britain in the 2nd century by Sarmatians and Alans. They find parallels for key features of the Arthurian legend, including the Sword in the Stone, the Holy Grail, and the return of Arthur’s sword to a lake, in the traditions of the Caucasus, and connect Arthur and his knights to Batraz and his Narts, the heroes of the legends of the North Caucasus.
Some Arthurian scholars have given credence to the Sarmatian connection, but others have found it based on conjecture and weak evidence. Few of the Caucasian traditions cited to support the theory can be traced specifically with the Sarmatians; many are known only from orally transmitted tales that are not datable before they were first recorded in the 19th century. Additionally, many of the strongest parallels to the Arthurian legend are not found in the earliest Brittonic materials, but only appear in the later Continental romances of the 12th century or later. As such, the traditions would have had to survive in Britain for at least a thousand years between the arrival of the Sarmatians in the 2nd century and the Arthurian romances of the 12th century. Nonetheless, the Sarmatian connection continues to have popular appeal; it is the basis of the 2004 film King Arthur.
I have read the excellent book by Geoffrey Ashe on Arthur, and consider it the most authoritative. I have also looked at the claim that the Bretons were “from Armenia”. I looked at the original Latin text and think that it is an actual scribal error, where ‘Armenia’ and “Armorica” were transposed. Many of the Bretons who joined William the Conqueror were actually former residents of Britain. That much said, I still see a case for Arthur being connected to Armenia. The common “AR” prefix, which means sun in Armenian is not conclusive proof in and of itself, but there is supporting cultural evidence of links between the ancient Britons and Armenians. Disclaimer: I was born in Britain and my wife’s family is Armenian.