He analysed 1,500 prehistoric sites in England and Wales and was able to connect all of them to at least two other sites using isosceles triangles - these are triangles with two sides the same length.
This, he says, is proof that the landmarks were deliberately created as navigational aides. Many were built within sight of each other and provided a simple way to get from A to B.
For more complex journeys, they would have broken up the route into a series of easy to navigate steps.
Anyone starting at Silbury Hill in Wiltshire, for instance, could have used the grid to get to Lanyon Quoit in Cornwall without a map.
Mr Brooks added: 'The sides of some of the triangles are over 100 miles across, yet the distances are accurate to within 100 metres. You cannot do that by chance.
At the link, you can see a map illustrating Brooks' hypothesis.
Link via Gizmodo
Image by flickr user Danny Sullivan used under creative commons license.
Well, there's the giveaway. You certainly couldn't do it by measurement in those days.