It was once thought the hill was a burial mound, but no grave has been found and its purpose is unknown.

BBC: Prehistoric Silbury Hill 'was built in layers'

The purpose, as Newman points out is to discover the unknown: a Trojan, or bot that has evaded detection and is sitting on some infected host.

FORBES: Uncovering the unknown threat via beaconing detection

The purpose of the current Okeanos Explorer expedition is to help reduce that large unknown, by mapping and imaging features and creatures that may never have been seen before.

WHITEHOUSE: Watch Live: Be a Virtual Ocean Explorer