Neil Fairbairn (in his Traveller's Guide to the Kingdoms of Arthur) says the site is also known as Cadon Barrow. It is the grave of Cador, an Earl of Cornwall and close friend of Arthur. Guinevere was supposed to have been living at his house/castle when Arthur met her.
In the Dream of Rhonabwy (in the Mabinogion) his name is spelt Cadwr, and he is named as the man responsible for arming Arthur as he goes into battle.
This is what Craig Weatherhill says about the barrow in “Cornovia: Ancient Sites of Cornwall & Scilly” (Cornwall Books - 1985, revised 1997 & 2000). “An excellent Bronze Age bowl barrow stands on a hilltop 300m above sea level. 26m across and 2.8m high, it is surrounded by traces of a wide ditch which has suffered from ploughing. An Ordnance Survey triangulation pillar stands on top of the barrow. The name ‘Condolden’ is derived from the Cornish ‘godolghyn’ (tump – a steep-sided mound); the alternative name, Cadon Barrow, is merely a contraction of Condolden.”