In 1946, an American archaeologist climbed onto a cattle pasture in southern Veracruz and counted five colossal basalt heads half-buried in the grass. The pasture was not a hill. It was the platform of the largest city in the late-second-millennium Americas. Seventeen of the heads have now been found — each one a different face, each one a person whose name is lost. They were carved three thousand years ago by people without a wheel, without a draft animal, and without a single metal tool, from stone dragged eighty kilometres across swamp and river. A sleep walk through the oldest civilization of the Americas, and the question that two hundred years of archaeology has not answered: how.

On a rainforest island in the western Pacific, ninety-two artificial islands rise from a shallow lagoon. They are built from columns of basalt, stacked log-cabin style, and the largest of them weigh fifty tons. The columns came from a quarry on the other side of the island — twenty-five miles away by sea. The people who built Nan Madol left no writing. Their descendants remember a flying dragon that carried the stones through the air. A sleep walk through the strangest stone city on Earth, and the question that nine hundred years of contact has not answered: how.

In 1549, a Spanish chronicler crossed the Andes and reached the ruins of a city near Lake Titicaca. He asked the local people who had built it. They told him the stones had appeared overnight — placed there by beings who came before the time of memory.

He believed they did not know. He may have been right.

Tiwanaku rose, flourished, and ended a thousand years before the Inca. It cut andesite with tolerances museums still measure. It fed a population of thirty thousand on land four kilometers in the sky. It traded with valleys five hundred kilometers away. And it left no name for itself that any later civilization preserved.

The city beside the lake.