Known today as the "West Country", Dyfneint encompassed Somerset, Dorset, Devon, and Cornwall, even possibly Breton lands at some point. The Dumnonii tribe ruled the greater part of this area. They were one of the largest and the most powerful British Celtic tribes. The Durotriges held the eastern parts of Dorset and Somerset, with the Belgae to the east of them, across the "border" in Llogres.

Exeter is usually considered the capital but since the Dumnonian royal families were always on the move, they likely had several different important places. There are numerous Iron Age Hillforts scattered about the area, usually surround by a number of farming settlements. Some of the best-preserved examples are Mai Dun (Maiden Castle), Chysauster and Carn Euny. The entire peninsula is liberally sprinkled with various prehistoric monuments, including standing stones, stone circles, burial mounds, chambered cairns, and the like. There are also the remnants of ancient mines, where tin, copper, lead and iron were extracted from the earth.

The Romans came in the middle of the first century, pushing westward and northward from Londinium. From fragmentary battle reports, they encountered significant resistance from the Durotriges. Bloody battles were fought at Maiden Castle and Hod Hill. In some cases, the hillforts were so well defended that the Romans had to lay siege to them and starve the inhabitants out. It is believed that, because of the strength of the Dumnonii, some sort of truce was negotiated, leaving them a measure of self-rule. Solidifying their conquest of the west, they built their forts at Exeter and Chester. From there, they "governed" Dumnonia, increasing mining operations and agricultural output, and setting up a busy trade.

After the Legions withdrew in the mid-400's, the bulk of Britain was easy pickings for the Saxons. However, it took over 300 years for them to finally conquer the Dumnonians. Allied with Viking Danes, the Celts resisted the advances of the Saxons in many bloody battles. Ecgberht of Wessex was unsuccessful in subjugating these people, in spite of having "laid waste the land from east to west". Dumgarth, the last of the Dumnonian kings, was drowned in 878. However, the country still did not fall completely under the yoke of the Saxons. Alfred, Edward the Elder, and Athelstan, continued to harry the Celts without any firm conclusion. In 936, Athelstan set the eastern bank of the River Tamar, as the boundary between Anglo-Saxon Wessex and the Celtic tribes to the west. Cornwall remained reasonably independent, probably through the paying of tribute, until the Norman Conquest. In 1066, Robert of Mortain was made Earl of Cornwall and built his castle at Launcestown.

The history of Cornwall under the Normans was much the same as that of the rest of Britain. Castles were built, occupied for a time, and then left to crumble. In spite of having foreign overlords, the Celtic people maintained their own style of living, customs and language. Sadly, the unique Brythonic language called Cornish was lost in the nineteenth century. However, the West Country has proudly maintained a Celtic identity that is still strong today and there are active efforts to revive the old language.
Contrary to the popular and romanticized versions of the Arthurian Legends, Tintagel Castle did not play an important part in history. The ruins which today stand on the rocky headland, were built in the thirteenth century by Richard of Cornwall, younger brother of Henry III. The site has absolutely no strategic value other than an imaginary association with the heroic kings of Britain. There are no Iron Age remains or prehistoric fortifications on this narrow spit of rock. The only evidence of earlier habitation is the monastic community of St. Juliot, which date from the sixth century.