Cornwall's early medieval setting is often discussed alongside Dumnonia, the broader south-western British kingdom associated with Cornwall and Devon. Dumnonia is therefore not simply another name for Cornwall. At Tintagel, archaeological work has revealed a prosperous settlement occupied between about AD 450 and 650, with buildings and imported goods connecting it to distant trading networks. These finds illuminate the wealth and contacts of the people who lived there. They do not identify a resident named Arthur, nor do they demonstrate that the events of a later romance occurred on the site.

Geoffrey of Monmouth gives Cornwall a central place in Arthur's beginnings. In his twelfth-century chronicle, Merlin enables Uther Pendragon to take the appearance of Gorlois and enter Tintagel, where Igraine is staying. Arthur is conceived during that deception. The story makes Cornwall essential to Geoffrey's royal narrative, but the surviving medieval castle is later. Richard, Earl of Cornwall, built it in the thirteenth century. English Heritage identifies the site's literary associations as an important explanation for his choice, while distinguishing his buildings from the much earlier settlement.

The Tristan romances supply another influential Cornish world. King Mark's marriage to Isolde and his relationship with Tristan vary across versions, from conflicted kingship to overt hostility. Their love story repeatedly draws meaning from a landscape of courts, woods, journeys and concealment. Castle Dore near Fowey later became associated with Mark's palace, although its supposed post-Roman hall was reassessed as Iron Age construction. That history of interpretation is part of the site's reputation; it does not turn the identification into an excavated royal biography.

The nearby Tristan Stone records Drustanus as a son of Cunomorus. Those names have encouraged comparisons with Tristan and Mark, but the inscription does not explicitly identify its people as characters from the romances. Its dating and original location also require care. Welsh tradition adds Celliwig in Cernyw as a court associated with Arthur. Cernyw is conventionally understood as Cornwall in that context, yet attempts to attach the literary court to a particular archaeological site remain uncertain. The stone, hillfort and court-name are valuable connections, not interchangeable proofs.

Cornish folklore extends Arthur's presence beyond royal courts and love stories. Later recorded traditions associate him with giants and striking features of the landscape, while Cornish language and place-names preserve connections with the wider Brittonic world. The age at which a story was collected does not by itself establish when it began. Cornwall can therefore be approached through several kinds of evidence at once: settlement remains, inscriptions, medieval texts and later folklore. Each contributes something different. The region is historical, while the identities and adventures attached to particular places must be understood through the sources that preserve them.