The oldest of English duchies (from 1337, though first a Norman earldom c.1140) has dimensions other than its peninsularity: the south‐flowing Tamar forms the county boundary with Devon. As the distant part of ‘civitas Dumnonia’ the Romans may not have colonized Cornwall, but they monopolized its tin production. For Cornish people England is entered by crossing the Tamar, and in the Civil War, though Cornish levies defended the crown within the county, they could not be brought to do so further east. Cornwall has a place in western prehistory at least as far back as the 3rd millennium bc, and in the 5th–6th cents. ad a church coloured by Irish and eastern Mediterranean practice; in later centuries it had a role not only in trade but in pilgrimage routes to southern Europe. In the 5th cent. ad Brittany received an immigration from Dumnonia (Britons), and the disused Cornish language may still be studied in Breton schools. Cornwall has had its share in the evolution of the Atlantic world. The Falmouth mail service developed a proud record on its American run 1688–1850, and in the 19th cent. Cornish miners worked, and died, in the mines of South America and South Africa; in 1901 Marconi, in Newfoundland, received the first transatlantic radio transmission from Poldhu near the Lizard. Back home, it had taken all Brunel's genius to bridge the Tamar at Saltash 1857–9, and so bring the railway, and a holiday industry, to Cornwall.
In antiquity tin from Cornwall's streams, increasingly deep‐mined by the later 16th cent., was the region's life‐blood. As ingots the metal was exported far and wide, but the earliest traders appear to have used the two north coast havens, St Ives‐Hayle and the Camel estuary: no place in Britain is so rich in the remains of 5th–6th‐cent. Mediterranean pottery as is Tintagel. Few, if any, British sites have more romance and mystery than this inhospitable headland: its history prior to the cliff‐hanging castle built there by Earl Richard of Cornwall in the 1230s is elusive, and associations with ‘King Arthur’ are solely attributable to the chronicler Geoffrey of Monmouth. At the time of Domesday Book (1086), in which neither Tintagel nor tin receive mention, Cornwall was evidently underpopulated. In 1346, however, Fowey was able to send over 40 ships to aid Edward III at Calais; in Armada year (1588) the port had only one ship in Queen Elizabeth's service, though Cornwall had become one of the most populous of southern counties. Its present‐day population is some 480,000, the most concentrated urban area being Redruth–Camborne. Truro (18,000) only became a centre in the early 19th cent., its cathedral, built 1890–1910, marking Cornwall as a diocese independent of Exeter for the first time.
The special status of the tin‐miners may have been established before the Conquest. When, in 1201, King John granted them their first charter confirming exceptional legal autonomies, in the Court of the Stannaries, agriculture in Cornwall needed to give way to the territorial requirements of the tin‐streamers; with the dukedom's establishment in 1336 their rights came under royal wardenship, though the court itself was only formally wound up in the mid‐19th cent. By the 16th cent. the leading county families, Rashleighs, Eliots, Godolphins, formed closely knit groupings to which the Tudor monarchs responded by granting enfranchisement to some fifteen additional boroughs, including Bossiney and Penryn, famed respectively for their slate and granite quarries. Their political evanescence may, however, be gauged by the Great Reform Act of 1832 which disfranchised almost all of them. But great houses, Lanhydrock, Cotehele, Trerice, still attest to aristocratic pride. Today, though the pilchard no longer thrives along their coasts and their deep mines are derelict, the Cornish retain their cultural richness. Britain and the wider world would be poorer without their artists and potters, their cream, and Mr Lemon Hart's rum.