Graham Robb’s new book has a remarkable opening. Taken unawares in his quiet Oxfordshire cottage, he is visited not by a person from Porlock, but by something quite the reverse: an idea so urgent and striking that it upturns his life and inspires his work. So vivid, indeed, that he speculates, ‘it would not have been surprising if some chronic state of historic hallucination had taken hold’.

Robb is planning a cycling trip along the Via Heraclea, ‘the fabled route of Hercules from the ends of the earth’ – actually from the southwest tip of the Iberian peninsula, over the Pyrenees and on towards the Alps. But a chance discovery suddenly gives his journey a whole new meaning, as if his GPS has lurched into mythic mode. He learns that his route directly aligns with the angle of the rising sun at the summer solstice. Connecting this fact with the existence of sixty locations between Britain and the Black Sea identified as Mediolanum – a Latin–Celtic conflation loosely meaning ‘sanctuary in the midst of the plain’, related to the ‘Middle Earth’ of myth – Robb realises he has stumbled on an extraordinary story: ‘A complex, beautiful pattern of lines emerged, based on solar alignments and elementary Euclidean geometry. I began to see, as though in some miraculously preserved document, the ancient birth of modern Europe.’

Why has no one seen this before? Robb’s answer is simple: they did not have access to the digital maps and mapping software that allowed him to open up this unknown world. The results threaten to overturn our preconceptions about an ancient people, especially those bequeathed by Roman propaganda. Far