Fifty years ago my mum said we might go and camp at Stonehenge and watch the sunrise on midsummer’s day. This sounded fun, and I dug out of a dusty cupboard what I thought was my dad’s wartime tent, but sadly turned out to be only a canvas chair, wide-bummed officers for the use of. We did go to Stonehenge for a picnic; we parked near a trilithon and sat on one of the fallen stones to eat our sandwiches. There were no fences, souvenir shops, druids, travellers, hippies, or police, but life was different then.

My interest was reawakened in 1965 by Gerry Hawkins’s book Stonehenge Decoded. Hawkins, a friendly chap whom I met some years later for lunch at the Explorer’s Club in New York City, had pulled off a clever trick. Computers were new in the mid-60s, and not generally available. So I and many others were amazed that he had got his hands on one and used it to investigate an ancient mystery. What was more, he claimed that his new computer revealed that Stonehenge was an old computer, built to record and predict dates.

 Stand behind one of the stones and look past the edges of it and another stone, and you see a point on the horizon. Hawkins fed the positions of the stones into his computer, and found many alignments which pointed to rising and setting points of sun and moon. Unfortunately there are so many alignments – 27,000 according to Hawkins - that they are bound to do so, just by chance; so even the most brilliant computer analysis can’t prove much.

 We still don’t know exactly why the stones were erected, although it seems mainly to do with the winter solstice. On the shortest day of the year – around 21 December - the sun rises exactly on several obvious sight-lines between the stones. To predict the exact day, year after year, would surely have been good for the street-cred of the priests. More important the agricultural community could then begin to think about planting new crops.

 What surprises me most about Stonehenge is not that the druids have claimed it for their own, but that the Christians have not done so. After all, they decided to attach the nativity story to the pagan midwinter festival; so why not claim that Stonehenge was an early Christian cathedral?