Constantine III of Britain

Constantine /ˈkɒnstəntin/ was a 6th-century king of Dumnonia in sub-Roman Britain, who was remembered in later British tradition as a legendary King of Britain. The only contemporary information about him comes from Gildas, who castigated him for various sins, including the murder of two "royal youths" inside a church. The historical Constantine is also known from the genealogies of the Dumnonian kings, and possibly inspired the tradition of Saint Constantine, a king-turned-monk venerated in Southwest Britain and elsewhere.

In the 12th century, Geoffrey of Monmouth included Constantine in his pseudohistorical chronicle Historia Regum Britanniae, adding details to Gildas' account and making Constantine the successor to King Arthur as King of Britain. Under Geoffrey's influence, Constantine appeared as Arthur's heir in later chronicles. Less commonly, he also appeared in that role in medieval Arthurian romances and in some modern versions of the legend.

Gildas mentions Constantine in chapters 28 and 29 of his 6th-century work De Excidio et Conquestu Britanniae. He is one of five Brittonic kings whom the author rebukes and compares to Biblical beasts. Gildas calls Constantine the "tyrannical whelp of the unclean lioness of Damnonia", a reference to the books of Daniel and Revelation, and apparently also a slur directed at his mother. This Damnonia is generally identified as the kingdom of Dumnonia in Southwestern Britain. Scholars such as Lloyd Laing and Leslie Alcock note the possibility that Gildas may have instead intended the territory of the Damnonii, a tribe in present-day Scotland mentioned by Ptolemy in the 2nd century, but others such as Thomas D. O'Sullivan consider this unlikely.

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