Given that it has become such an icon of the pre-Columbian world that the Spanish destroyed, it seems extraordinary that we have only known of Machu Picchu for 100 years.

When the US explorer and Yale academic Hiram Bingham arrived in the Peruvian Andes in July 1911, he was ready for what was to be the climactic achievement of his life: the exploration of the remote hinterland to the west of Cusco, the old Inca capital. He had every advantage on his side, with his charisma, opportunism, knowledge of bibliographical sources and driving, restless energy. Above all, he had what every explorer needs--luck and the ability to exploit it.

Bingham had already done a preliminary reconnaissance a few years before, in 1909, when he had made the mistake of coming during the wet season. This time, he would be on dry ground, and he had prepared meticulously for it, both with a well-provisioned Yale team and with the invaluable research he had been given by a Peruvian academic, Carlos Romero, and by Sir Clements Markham, the former president of the Royal Geographical Society, who had just published his groundbreaking The Incas of Peru. Both Romero and Markham had recently discovered chronicles from the time of the Spanish Conquest that pointed to the existence of hitherto unsuspected Inca ruins.

Despite all of this, Bingham could never have anticipated quite what lay ahead. In the space of just a few short months, he was to discover Machu Picchu, by any standards one of the greatest architectural achievements of pre-Columbian civilisation, and also two other major sites: Vitcos, where the last Incas retreated after the Spanish had conquered the rest of their empire and which was to become their capital in exile for a further 35 years; and another mysterious site down below in the jungle, whose significance evaded Bingham at the time, in an area he called the Plain of Ghosts.

NEW ROUTE

Cusco, the ancient capital of the Incas, lies on a high plateau on the edge of the Andes at an elevation of more than 3,000 metres. Bingham's plan was to descend from this plateau along the valley of the Urubamba. This river weaves a circuitous route west, north and finally east of Cusco to reach the Amazon, passing through the quadrant of dramatically plunging canyons and broken mountain ranges known as the Vilcabamba.

When Bingham and his team set off down the Urubamba in 1911, they had an advantage over travellers who had preceded them: a mule trail had recently been blasted down the valley canyon to enable rubber to be brought up more easily from the jungle. Almost all previous travellers had left the river at Ollantaytambo and taken a high pass across the mountains by Mount Ver6nica to rejoin the river lower down, thereby cutting a substantial corner but also therefore never visiting the area around Machu Picchu. This was as much for convenience as for the difficulties of negotiating the river descent before the road was...