Constantyn, Constaunce, Costaunce, Costauns
Arthur’s successor whom Geoffrey of Monmouth makes a cousin, taking the name and a few particulars from Gildas, who denounces a king so called. Gilda’s Constantine ruled only in Damnonia (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, disguised as an abbot. “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.
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. There was an historical minor king, Constantine of Dumnonia (Devon) in the early sixth century, though he was a murderous deceitful king.
Sources
De Excidio et Conquestu Britanniae | Gildas, c. 540
Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138
Roman de Brut | Wace, c. 1155
Brut | Layamon, late 12th century to mid-13th century
De Casibus Virorum Illustrium | Giovanni Boccaccio, 1355-1362
Alliterative Morte Arthure | c. 1400
Le Morte Darthur | Sir Thomas Malory, 1469-1470