In his book The Silbury Treasure Michael Dames identifies the Great Barrow as a possible Harvest Hill (like Silbury but smaller) because of it’s size and proximity to Knowlton Henge:
Knowlton itself is 20 feet high, and surrounded by two concentric ditches (the outermost being 354 feet in diameter and 34 feet across)... The majestic scale of the edifice disqualifies it as a Bronze Age barrow, and since Neolithic barrows in Dorset are long, not round, a harvest hill function is a reasonable provisional attribute. Thus, though the Knowlton mound is called the Great Barrow, it is not at all likely to contain a burial except perhaps as a secondary internment, inserted at a later age.