|Unfortunately, a very low-res image.
From the Castle Explorer site:
Tintagel Castle is set on a dramatic and picturesque headland that is virtually an island, connected to the mainland by a slim finger of land. Over the centuries much of the castle has fallen into the sea and very little remains today, but it is worth the steep climb up the steps to either part of the castle for the setting alone.
The headland has been linked with the tales of King Arthur since 1136, when Geoffrey of Monmouth wrote that it was here that King Arthur was conceived. Later stories told of how Arthur was born and even lived at Tintagel, but there is no direct evidence to connect him with the area. However, the remains of a large 5th and 6th century settlement and the quantity of imported luxury goods found, suggest that this may have been a stronghold of the kings of Dumnonia - a kingdom comprising Cornwall, Devon and parts of Somerset. During this time a large defensive ditch was dug, effectively cutting off access to the headland, and helping give Tintagel its name - Din Tagell, the Fortress of the Narrow Entrance.
In 1233, Richard, Earl of Cornwall, acquired Tintagel and built a castle on the headland. The location was not ideal for building a castle and the area had no strategic value, so we have to presume that Richard probably wanted to associate himself with the already popular Arthurian legends. Later Earls of Cornwall made little use of the castle, leaving it in the care of a constable, and by the late 15th century the castle was already in ruins.
From the Wikipedia:
Major excavations beginning with Ralegh Radford's work in the 1930s on and around the site of the 12th century castle have revealed that Tintagel headland was the site of a high status Celtic monastery (according to Radford), a princely fortress or trading settlement dating to the 5th and 6th centuries, in the period immediately following the withdrawal of the Romans from Britain. Finds of Mediterranean oil and wine jars show that Sub-Roman Britain was not the isolated outpost it was considered to be, for considerable trade in high value goods was taking place at the time with the Mediterranean region. In 1998, excavations descovered the "Arthur stone" which has added to Tintagel's Arthurian lore.