1. Constantine
      Constans, Constance, Constant, Constantin, Constantins, Constantius, Custenhin

      Ruler of Brittany and Arthur’s grandfather, found earliest in Geoffrey of Monmouth. Constantine was the brother of Aldroen (Aldroenus). A prince from the offshoot British kingdom in Armorica (given an unhistorically early foundation), he comes to Britain by invitation near the beginning of the fifth century, to organize defense against marauding barbarians. Completely successful, he is rewarded with the crown.

      Father of Constans, who becomes a monk, Ambrosius Aurelius, and Uther Pendragon (or Maine, Pendragon, and Uther, as Robert de Boron and the Vulgate Merlin have it), the future father of Arthur. Constantine's father may have been named Tahalais (Thailais), though Baudin Butor makes him the son of Londres. Butor is the only writer to name Constantine’s wife: Ivoire, sister of King Ban.

      When Guethelin, Archbishop of London, came to Brittany to seek help in driving the Picts and Huns from Britain, Constantine agreed to accomplish the tasks. He traveled to Britain and destroyed the barbarians. Then, since their was no other suitable candidate, he was crowned king at Silchester. In the original accounts, Constantine ruled for ten years before he was assassinated by one of his servants - a Pict named Cadal (or, in some texts, by Vortigern himself); but the Vulgate Merlin purports that he died of old age. The crafty Vortigern, the Earl of Gwent, persuades Constans to leave his monastery and become king. Constans is a puppet in Vortigern's hands, and presently he, too, is assassinated. Suspicion falls on Vortigern. Constantine's other sons are still children, and their guardians take them to the Breton court for safety. Vortigern seizes the crown. When the princes are grown up, however, they return and depose him, so that the royal house continues, producing Arthur in the next generation.

      Constantine is based on a historical Roman army soldier who served in Britain. His story is given by Bede. In 407, his troops elected him "Emperor Constantine III" of Rome - despite the existence of a legitimate Roman emperor named Honorius - and he embarked for the continent on a war of acquisition. After conquering Gaul and Spain, he surrendered in 411 to the legitimate Roman army and the general of Honorius. and was soon murdered. Like the fictional Constantine, he apparently had a son named Constans who left a monastery, but who was already dead at the time of Constantine’s murder. The historical character survives in the accounts of Nennius and William of Malmesbury, and in a second Constantine mentioned by Geoffrey of Monmouth, but with legendary embellishments. Nennius thought that he was the King of Britain before Vortigern, though he gives a fairy accurate account of his continental exploits and his death. Geoffrey’s second King Constantine, who preceded Arthur’s grandfather, actually managed to conquer Rome from the Emperor Maxentius, but found his British throne usurped by Octavius.

      Constantine III's removal of troops from Britain was a prime cause of its severance from the Empire, which occured in 410. Left unprotected against the assaults of Saxons and other barbarians, the Britons turned against him. Honorius authorized them to arm in their own defense, with the result that they became self-governing. Geoffrey's independent fifth-century Britain is founded, to that extent at least, on historical fact.

    2. Constantine
      Constantyn, Constaunce, Costaunce, Costauns

      Arthur's successor. Geoffrey of Monmouth makes him a cousin, taking the name and a few particulars from Gildas, who denounces a king so called. Gilda's Constantine ruled only in Dumnonia, now known as the West Country. His conversion into a king of all Britain is incompatible with any historical possibility.

      A son of Cador (sometimes called Carados) of Cornwall, he was a Knight of the Round Table and Arthur’s cousin or nephew, a close and trusted knight. Arthur left him and Sir Baudwin of Britain as joint governors of the realm during his continental war with Emperor Lucius of Rome, and Constantine was therefore in position for the crown when Arthur died without an heir. Geoffrey of Monmouth says that Arthur gave him the crown after the battle of Camlann, of which Arthur and Constantine were the only survivors. In Jean D’Outremeuse’s Ly Myreur des Histors, it is Lancelot who places Constantine on the throne. He tried unsuccessfully to keep Sir Bors, Ector de Maris, Blamore, Bleoberis, and other former companions of the Table with him in England after Lancelot's death. Malory reports that he was a good king, restored the Archbishop of Canterbury to his diocese, and restored order to the realm. Geoffrey says that he faced problems with the Saxons and with the two sons of Mordred, but was able to overcome them. When Mordred’s sons took refuge in churches, Constantine pursued them and killed them before the altars. "Smitten by God’s judgment" for this sacrilege, Constantine was killed by his nephew Conan, who succeeded him.

      Still, even allowing for the fact that the flower of Arthur's knighthood was either slaughtered or moved to Gaul and/or hermitages during and after the wars with Lancelot and Mordred, it does seem that the man who eventually succeeded Arthur must have been a person of some importance. Arthur would have done better to have reappointed Constantine governor, instead of Mordred, when he went to fight Lancelot in France.

      There was an historical king Constantine of Dumnonia (Devon) in the early sixth century, though he was a murderous, deceitful king.

    3. Constantine
      Custenhin, Custennin

      Son of Mynwyedig and father of Goreu in Culhwch and Olwen. Constantine was the shepherd of Ysbaddaden, the giant father of Olwen, and he gave lodging to Culhwch and his party during their visit to Ysbaddaden’s realm.

      He was apparently married to one of Culhwch’s aunts. Ysbaddaden had slain twenty-three of his sons, so he kept the last, Goreu, hidden in a chest. The Triads call him Arthur’s cousin. This identification plus his residence in Cornwall suggests that he is a Welsh prototype of Constantine2.

    4. Constantine

      Father of Erbin and grandfather of Geraint.

    5. Constantine III

      Constantine was a minor king in the sixth century Britain, who in later tradition was remembered as a legendary king of Britain.

      Gildas calls him king of Damnonia (Dumnonia) in his De Excidio et Conquestu Britanniae. He is said to have performed several sins, for example, he murdered two praying youths, of royal descent, inside a church, disguised as an abbot.

      He is remembered in Historia Regum Britanniae, written by Geoffrey of Monmouth, whom makes him King Arthur's successor.

      In Bonedd y Saint he is said to be the father of Erbin. He is identified, by scholars, with Custennin Gorneu or Custennin Corneu ('Constantine of Cornwall') who is found in the genealogies of the kings of Dumnonia.

    6. Constantine III
      Constantine II, Flavius Claudius Constantinus
      Died 18 September 411

      A Roman general who, in 407, declared himself Western Roman Emperor in Britannia, and lived in Gaul. In Arthurian tradition he succeeded king Gracianus Municeps (Gratian) when the latter was assassinated. In some versions, his seneschal was Vortigern.