Stone Age Tom Toms
1,500 sites stretching from Norfolk to north Wales. These included standing stones, hilltop forts, stone circles and hill camps. Each was built within eyeshot of the next.
Using GPS co-ordinates, he plotted a course between the monuments and noted their positions to each other.
He found that they all lie on a vast geometric grid made up of isosceles 'triangles'. Each triangle has two sides of the same length and 'point' to the next settlement.
The centre of the whole network is Silbury Hill and one of the nearest points is Rybury Camp which is south of it. You would think he must have examined it really well as his whole network depends on the first points.
The top of Silbury Hill is 187 metres; your task today is to work out how you can stand there and see the top of Rybury Camp (240 m) through the Tan Hill ridge which at its lowest is 255 m. Maybe Stone Age man had really tall periscopes as well...