History and legend are inseparable at Tintagel. From about the 5th to the 7th century AD it was an important stronghold, and probably a residence of rulers of Cornwall. Many fragments of luxury pottery imported from the Mediterranean were left behind by those who lived here. It was probably memories of this seat of Cornish kings that inspired the 12th-century writer Geoffrey of Monmouth to name it in his History of the Kings of Britain as the place where King Arthur was conceived, with the help of Merlin. At the same time, Cornish and Breton writers linked the love story of Tristan and Iseult with Tintagel. In turn, these associations with legend led the hugely rich and ambitious Richard, Earl of Cornwall, to build a castle here in the 1230s. The site was of no military value – legend alone seems to have inspired him to build here. And long after the castle had fallen into decay, its mythical associations kept interest in Tintagel alive.
In 1225, Richard, 1st Earl of Cornwall traded with Gervase de Tintagel, swapping the land of Merthen (originally part of the manor of Winnianton) for Tintagel Castle. A castle was built on the site by Earl Richard in 1233 to establish a connection with the Arthurian legends that were associated by Geoffrey of Monmouth with the area and because it was seen as the traditional place for Cornish kings. The castle was built in a more old-fashioned style for the time to make it appear more ancient. . . . John Holland, 1st Duke of Exeter was appointed constable of Tintagel Castle in 1389. After Richard, the following Earls of Cornwall were not interested in the castle, and it was left to the High Sheriff of Cornwall. Parts of the accommodation were used as a prison and the land was let as pasture. The castle became more dilapidated, and the roof was removed from the Great Hall in the 1330s. Thereafter, the castle became more and more ruinous and there was progressive damage from the erosion of the isthmus that joined the castle to the mainland.