A straight line between SH, SM and MM? That's interesting, though if all three mounds were for festive as well as for religious occasions they would not necessarily need to be aligned. Just to be clear though, Silbury Hill and the Marlborough Mound appear to be two structures of a similar size and shape but do they date from around the same time?

The Silbury Mound may be similar in shape to Silbury Hill and the Marlborough Mound but we don't know that for sure yet let alone whether it's earlier or later than SH or MM.

Are there any more Silbury-type structures in the area?