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Megaliths around the world – from Stonehenge to Sacsayhuaman – have intrigued the modern world, with an air of mystery surrounding their construction, and their function.

So what then do you think people of future millennia might imagine the monolithic ‘sound mirrors‘ that haunt the coastline of southern England were used for? Not even a century after their construction, most of the general public would have little idea when, or for what purpose, they were built.

For the record, there are a number of sound mirrors dotted along the southern coast of England. Just as the moai of Easter Island gaze silently out into the Pacific Ocean [edit: I’ve been informed I’m wrong on that: the moai actually face inland to the island’s volcano – thanks rolandr], these modern English megaliths also face out into another body of water: the English Channel. Their function, however, was not to look, but to listen.

They were constructed in response to a ground-breaking invention: the aircraft. With World War I came the realisation that England was no longer protected by the Channel, but could be attacked from the air. These odd-shaped concrete constructions were constructed as an early-warning system: shaped to reflect and focus the sound of incoming aircraft (within a range of around 25 miles) to observers, they would allow authorities to deploy counter-measures in a timely manner (warning the population, and attacking the incoming aircraft).

Unfortunately, however, rapid advances in the speed of aircraft, and the development of radar in the 1930s, meant that the sound mirrors were made obsolete within a decade of their construction. But they still remain in various locations along the British coastline, just waiting to one day be forgotten, before having new mythologies attached to them…

(thanks Norman)