Around 6000 BC a revolution took place on Orkney and the Western Isles of Scotland. An outstanding collection of stone circles, standing stones, round towers and passage mounds appeared seemingly out of nowhere. And yet many such monuments were not indigenous to Britain, but to regions of the Caspian Sea and the Mediterranean. Their creators were equally mysterious. Traditions tell of the Papae and Peti, 'strangers from afar' who were physically...