It is the year 1491. America is a vast land with vast resources. Millions of bison roam beside huge forests, the waters are teeming with fish, and in the sky huge flocks of birds block out the sun. But America is not a pristine wilderness. It is an old continent, inhabited by a hundred million people. They live in complex urban societies that know little of each other. Some of them are expanding, others declining. On the Upper Mississippi River Valley is Cahokia, one of the continent's largest civilisations. From atop the Andes, the Inca rule a kingdom of six million. In the Amazon basin, the Beni people flourish. They have built a vast infrastructure of earthworks, orchards, canals and causeways. These peoples all have sophisticated agricultural techniques. They grow crops and domesticate animals unknown to the rest of the world.