Corineus... following in this the example of his leader, called the region of the kingdom which had fallen to his share Cornwall, after the manner of his own name, and the people who lived there he called Cornishmen. Although he might have chosen his own estates before all the others who had come there, he preferred the region which is now called Cornwall, either for its being the cornu or horn of Britain, or through a corruption of his own name. [I.16]

CORNWALL appears first in the Historia as the region of Britain which Brutus's companion Corineus claims as his own. It then appears in the ongoing struggles, early in the work, over control of the whole island:

Some time later a certain young man called Dunvallo Molmutius came into prominence because of his personal courage. The son of Cloten King of Cornwall, he excelled all the other kings of Britain by his good looks and his bravery. Almost as soon as he had succeeded to the kingship of Cornwall after his father's death, he attacked Pinner, King of Loegria, and killed him in a pitched battle. [II.17]

Belinus and Brennius, the two sons of Dunvallo, each of whom was determined to inherit the kingship, now began a great war of attrition against each other.... at length their friends intervened to make peace between them. These friends decided that the kingdom should be divided between the two of them in such a way that Belinus should be crowned King of the island and hold Loegria, Kambria and Cornwall, he being the elder.... [III.1]

One of the roads built by Belinus to link the whole realm of Britain together ran from the Cornish Sea to the shore of Caithness [III.5]. Cornwall also features when the realm is converted to Christianity:

Loegria itself was placed under the Metropolitan of London, together with Cornwall. The Severn divides these last two provinces from Kambria or Wales, which last was placed under the City of Legions. [IV.19]

Gorlois, duke of Cornwall, retreats to his castle at Tintagel when Uther Pendragon desires Ygerna, and it is in Tintagel Castle that the disguised Uther tricks Ygerna and thus fathers Arthur.

The losses were greater in Mordred's army and they forced him to fly once more in shame from the battle-field. He made no arrangements whatsoever for the burial of his dead, but fled as fast as ship could carry him, and made his way towards Cornwall. Arthur was filled with great mental anguish by the fact that Mordred had escaped him so often. Without losing a moment, he followed him to that same locality, reaching the River Camblan... [XI.2]

The Tintagel Castle website includes a History and Research section that outlines archaeological work that has been carried out at the site.

While some writers have suggested Camboglanna, a fort on Hadrian's wall, as the site of Arthur's final battle, it is clear that in Geoffrey it occurs in Cornwall. Click CAMELFORD on the map for more information.

Finally, Cornwall becomes, like Wales (KAMBRIA), a place of refuge for the Britons suring the Saxon invasions:

Once this inhuman tyrant Gormund, with his countless thousands of Africans, had destroyed almost all the island... he handed over a considerable part of it, called Loegria, to the Saxons.... Such Britons as remained sought refuge in the western parts of the kingdom: that is, in Cornwall and Wales. [XI.10]

For eleven years Britain remained deserted by all its inhabitants, except for a few whom death had spared in certain parts of Wales.... [The Saxons] landed in parts of Northumbria and occupied the waste lands from Albany to Cornwall. There was no local inhabitant left alive to stop them, except for a few little pockets of Britons who had stayed behind, living precariously in Wales, in the remote recesses of the woods. From that time on the power of the Britons came to an end in the islands, and the Angles began to reign. [XII.16]

Cornwall appears in Merlin's Prophecies:

A Wolf will act as a standard-bearer and lead the troops, and it will coil its tail round Cornwall. A soldier in a chariot will resist the Wolf and transform the Cornish people into a Boar. As a result the Boar will devastate the provinces, but it will hide its head in the depths of the Severn. [VII.4]