"Wow," exclaims the visitor from New Zealand, a place, after all, with a human history shorter than most. For from a wooden walkway we’re gazing down at an archaeological site of giddying age. Built about 9000 BC, it’s more than twice as old as Stonehenge or the Pyramids, predating the discovery of metals, pottery or even the wheel. This is Göbekli Tepe in south-eastern Turkey, generally reckoned the most exciting and historically significant archaeological dig currently under way anywhere in the world, and there are neither queues nor tickets to get in. Wow for a number of reasons, then, though...