Take yer pick. .

A pregnant belly
A tomb for 'Lord Sil'
A Mother earth breast
An earth energy conductor
A prototype pyramid
A flying saucer landing pad

One thing I do know, when Julian called it the 'all seeing eye' I know what he meant. It keeps popping up wherever you travel around that landscape.
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The Wagon & Horses used to do a 'Silbury Special' a while back. Brown bread 'mound', with cheese and onion and pinaple in it, served with chips and salad. It was supposed to look like Silbury. It didn't . . . but tasty after a hard days feildwork it was!!!!