William Camden, in his 1607 edition of Britannia, describes Cornwall and Devon as being two parts of the same 'country' which:was in ancient time inhabited by those Britains whom Solinus called Dunmonii, Ptolomee Damnonii, or (as we find in some other copies) more truly Danmonii.

Amédée Thierry (Histoire des Gaulois, 1828), one of the inventors of the historic race of Gauls, could confidently equate them with the Cornish ("les Cornouailles").

The people of Dumnonia spoke a Southwestern Brythonic dialect of Celtic similar to the forerunner of more recent Cornish and Breton.

[4] Tristram Risdon suggested the continuance of a Brythonic dialect in the South Hams, Devon, as late as the 14th century, in addition to its use in Cornwall.

The name purocoronavium that appears in the Ravenna Cosmography implies the existence of a sub-tribe called the Cornavii or Cornovii, perhaps the ancestors of the Cornish people.

Gaius Iulius Solinus, probably in the 3rd century, remarks: "This turbid strait also divides the island Silura from the shore which is held by the Dumnonii, a British tribe.

"[6] In the sub-Roman period a Brythonic kingdom called Dumnonia emerged, covering the entire peninsula, although it is believed by some to have effectively been a collection of sub-kingdoms.

This oppidum (a Latin term meaning an important town) on the banks of River Exe certainly existed prior to the foundation of the Roman city in about AD 50.

Isca Dumnoniorum originated with a settlement that developed around the Roman fortress of the Legio II Augusta and is one of the four poleis (cities) attributed to the tribe by Ptolemy.

Near Padstow, a site of some importance that was inhabited from the late Bronze/early Iron Age to the mid 6th century now lies buried under the sands on the opposite side of the Camel estuary near St. Enodoc's Church, and may have been a western coastal equivalent of a Saxon Shore Fort.

These seem to have survived the Roman abandonment of Britain, but were subsequently replaced, in the 6th and 7th centuries, by the unenclosed farms taking the Brythonic toponymic tre-.

[15] The earliest account of Cornish tin mining was written by Pytheas of Massilia late in the 4th century BC after his circumnavigation of the British Isles.

Tin working continued throughout Roman occupation although it appears that output declined because of new supplies brought in from the deposits discovered in Iberia (Spain and Portugal).

The main sources available for discussion of this period include Gildas's De Excidio Britanniae and Nennius's Historia Brittonum, the Annales Cambriae, Anglo-Saxon Chronicle, William of Malmesbury's Gesta Regum Anglorum and De Antiquitate Glastoniensis Ecclesiae, along with texts from the Black Book of Carmarthen and the Red Book of Hergest, and Bede's Historia ecclesiastica gentis Anglorum as well as "The Descent of the Men of the North" (Bonedd Gwŷr y Gogledd, in Peniarth MS 45 and elsewhere) and the Book of Baglan.