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It is a chilly morning in spring, around the year 3000 BC, on a plane in southern England.

A herd of Borax cattle, each one the height of an adult man, grazes on fresh green shoots.

Keeping their distance from the huge, horned beasts, a family dressed in animal skins walks

in procession across the plane. Their dogs bound through the dewy grass, their goat tugs

on its rope, a young child rides on her father's shoulders. Their leader is a grandmother who

shields her eyes against the bright sun. Her clan live in the vast forest that blankets

the land, and to them this wide open space is unusual and startling. But you can make

out their destination on the horizon. A strange, white curve on the land, encircling a group

of tall, upright posts, like trees without branches or leaves. One of her dogs pricks its

ears, alerted by voices on the wind. The other one barks. She calls them back with a whistle.

Another strange feature of this place is how far voices can carry. At least she hopes

to do so. When she hears the rhythmic crack of stone hitting stone, she is reassured

that the noises are human. They walk on. The sun is at its zenith as they approach their

destination and start to make out the figures of people working ahead. The travelers stop

and stare. There are more people than they have ever seen before. Women in the bottom

of a deep circular galley are digging with axes made of deer antlers. Men haul baskets

...