In Brampton, Cumbria, there is a hill shown on the OS as a Motte. It's covered in beech trees which disguise its presence - I've no pictures of it (perhaps RockNicker might catch it) - but it is roughly the same size as Silbury Hill. There's a tiny one, also shown as a Motte, that Hob and I have discussed, at Eals, Northumberland. There must be lots of lost prehistoric mounds.

The therapeutic model of Silbury I built of green woodland product, two metres tall, a week ago, has just started steaming.

Yes, I remember the discussions. Bit of a puzzle, Isn't it?