How far did the horizons of our first ancestors extend? In the furthest past, even the nearest ridge of hills might then have disclosed a sight no human eyes had ever seen, and every river crossed was a ford into the unknown. The Palaeolithic and Mesolithic were eras when all was a great trek, all an act of discovery and endurance. Yet there is one frontier we do not so often associate with the distant past today, one even greater, and more imposing, than the primordial steppes and forests: t...
