Lost Cities of the Amazon

A For most of the twentieth century, the Amazon rainforest was pictured as a pristine wilderness, a green ocean of trees almost untouched by human hands. Scholars argued that its thin, acidic soils could never have supported large or settled populations, and that the scattered groups living there today were the remnants of people who had always been few and always on the move. The forest, in this view, was a natural cathedral that civilisation had never entered. The very lushness of the vegetation was taken as proof of its emptiness, for surely, it was argued, land rich enough to grow such giant trees would long ago have been cleared and farmed had large numbers of people ever settled there.

B This picture sat awkwardly with an old and troubling report. In 1542 the Spanish soldier Francisco de Orellana became the first European to travel the length of the Amazon, and the chronicle of his voyage described banks crowded with people, fields stretching inland and towns strung along the river for mile after mile. For centuries these claims were treated as tall tales, the exaggerations of a desperate expedition trying to make its sufferings sound grander. Surely, critics said, such a poor land could never have held such multitudes. The expedition's chronicler wrote of well-defended towns and of roads leading away inland, but his report was easy to dismiss, for the Spaniards never returned to those places and no ruins of stone cities were ever found standing above the trees.

C In recent decades new tools have forced a reappraisal. The most powerful is airborne laser scanning, or LIDAR, which fires pulses of light from an aircraft and measures how long they take to bounce back. Enough of these pulses slip between the leaves to reach the ground, allowing researchers to strip away the canopy on a computer and reveal the bare earth beneath. Where the eye saw only forest, the laser has exposed a hidden geometry of raised platforms, ditches, geoglyphs and dead-straight causeways linking one settlement to the next. In parts of the Bolivian lowlands and the upper reaches of the basin, these surveys have exposed whole networks of mounds, reservoirs and avenues laid out with obvious care, the unmistakable fingerprints of large and organised communities.

D A second clue lies in the soil itself. Across large areas of the basin, patches of unusually dark, fertile earth can be found, quite unlike the pale ground around them. Known as terra preta, or dark earth, this soil is not natural but was created by people who enriched it with charcoal, ash, bones and household waste over many generations. Its very existence implies dense, stable communities large enough to transform the land they lived on, and productive enough to feed themselves from it year after year. Remarkably, terra preta remains fertile to this day, long after the people who made it disappeared, and modern farmers prize the patches they come across, while scientists study them in the hope of learning how such long-lasting soils were created.

E If such societies existed, why did they vanish so completely? The answer appears to be catastrophe. When Europeans arrived, they brought diseases to which the inhabitants had no resistance, and epidemics swept through the population with terrible speed, often running ahead of the newcomers themselves. Within a century the great riverside communities had collapsed, their fields were abandoned, and the fast-growing forest reclaimed the clearings, swallowing houses, roads and monuments beneath a fresh blanket of trees. So complete was this green burial that later travellers passed directly over the remains of once-teeming settlements without noticing a thing, which is why the old tales of a crowded Amazon came, for so long, to seem like pure invention.

F The result is a strikingly different understanding of the region. Far from being a virgin wilderness, much of the Amazon now looks like a landscape shaped over thousands of years by human beings, a mosaic of managed forests, orchards and garden cities. Some researchers even argue that the mix of useful plants growing there today is partly a living legacy of ancient cultivation. The forest, it turns out, may be less a thing that people never touched than a thing that people helped to make. If that is so, then protecting the Amazon may mean recognising it not simply as a wilderness to be left alone, but as an inheritance long tended by human hands.