Cadbury Castle has a flat top of 18 acres with a perimeter of 3/4 of a mile. It's only twelve miles south of Glastonbury, Somerset, one of the few real places named in the Arthurian legends, and very close to the Fosse Way, the Roman road from Lincoln to Exeter. This ties in with Camelot's standing as a last outpost of Roman civilisation in a barbarian world.
A major archaeological excavation from 1966 -70 reinforced Cadbury's claim to have been the most probable site of Camelot. It revealed that this Iron Age hill fort was occupied as early as the 4th millennium BC, unused during the Roman period but then refortified by a major British ruler and occupied for a century from about 470 AD. This grandiose conversion during the Arthurian era into a vast and important citadel had 16 feet thick defensive walls, by far the largest known British fortifications of the time. The fortress must therefore have been an important pre-Saxon king's capital.
Knight for a Day locates Camelot at Cadbury Castle in 533 AD, in the light of best current archaeological and historical knowledge about the sub-Roman era in southwest England and the local geography.