Which ancient civilization built Machu Picchu?

The Inca, around 1450, probably as a country estate for the emperor Pachacuti rather than a city or a fortress. It held perhaps 750 people and was abandoned within about a century, at the time of the Spanish conquest - though the Spanish never found it, which is why it survived intact when almost everything else was dismantled for its stone.

The stonework is the thing that stops people. The finest walls are fitted without mortar, blocks shaped to match their neighbours so precisely that a knife blade will not go between them, and slightly inclined inward with trapezoidal doors and windows. This is earthquake country, and in a quake the stones are said to dance and resettle. Around sixty per cent of the construction is underground - terracing and layered drainage that is why a site built on a steep slope in a place with two metres of annual rainfall has not slid down the mountain.

It was not lost, and Hiram Bingham did not discover it in 1911. Local families were farming the terraces and led him there, and their names are in his own notes; earlier visitors had left graffiti. What Bingham did was publicise it, and remove thousands of artefacts to Yale, which returned them only after a legal dispute settled in 2011.