The ancient settlers of the Americas migrated from Asia, though their timing and their route are debated. One possibility is that the first settlers migrated across the Bering Strait from what is now Russia to Alaska and gradually migrated southward sometime between 15,000 and 13,000 B.C.E. But archaeological excavations have identified much earlier settlements, perhaps dating to over 40,000 years ago, along the Andes in South America than they have for Mesoamerica or North America. These findings suggest that the original settlers in the Americas arrived instead (or also) as fishermen circulating the Pacific Ocean.

Like early settlers elsewhere in the world, populations of the Americas could be divided into three categories: nomadic peoples, semi-sedentary farming communities, and dense agricultural communities capable of sustaining cities. Urban settlement and empire formation centered around two major regions. The first area was Lake Titicaca, located at the present-day border between Peru and Bolivia. The second area was in the Valley of Mexico on the central plateau of Mesoamerica, where empires emerged from the cities around Lake Texcoco. Access to these large freshwater lakes allowed agriculture to expand through irrigation, which in turn supported large urban populations.

The earliest farming settlements emerged around 5000 B.C.E. These farming communities began the long process of domesticating and modifying plants, including maize (corn) and potatoes. The origins of maize in Mesoamerica are unclear, though it became a centerpiece of the Mesoamerican diet and spread across North and South America. Eaten together with beans, maize provided Mesoamerican peoples with a diet sufficient in protein despite the scarcity of meat. Mesoamericans processed kernels through nixtamalization, boiling the maize in a solution of water and mineral lime. The process broke down compounds in the kernels, increasing their nutritional value, while enriching the resulting masa, or paste, with dietary minerals including calcium, potassium, and iron.

This masa could be rolled flat on a stone called a metate and baked into tortillas. Tortillas played roles similar to bread in wheat-producing cultures: they could be stored, they were light and easy to transport, and they were used as the basic building block of meals. Aztec armies of the fifteenth century could travel long distances because they carried tortillas for sustenance.

Andean peoples cultivated another staple of the Americas, the potato. Potatoes first grew wild, but selective breeding produced many different varieties. For Andean peoples, potatoes became an integral part of a complex system of cultivation at varying altitudes. Communities created a system of “vertical archipelagos” through which they took advantage of the changes of climate along the steep escarpments of the Andes. Different crops could be cultivated at different altitudes, allowing communities to engage in intense and varied farming in what would otherwise have been inhospitable territory.

Communities raised multiple crops and engaged in year-round farming by working at different altitudes located within a day’s journey from home. Some of these zones of cultivation were so distant — sometimes over a week’s journey — that they were tended by temporary or permanent colonies, called mitmaq, of the main settlement.

At higher elevations, members of these communities cultivated potatoes. Arid conditions across much of the altiplano, or high-plains plateau, meant that crops of potatoes could sometimes be planted only every few years. But the climate — dry with daily extremes of heat and cold — could be used to freeze-dry potatoes that could be stored indefinitely. Above the potato-growing zone, shepherds tended animals such as llamas and alpacas.

At middle altitudes, communities used terraces edged by stone walls to extend cultivation along steep mountainsides to grow corn. In the lowlands, they cultivated the high-protein grain quinoa, as well as beans, peppers, and coca. In the lowlands communities also grew cotton, and in coastal areas they harvested fish and mussels. Fishermen built inflatable rafts made of sealskin.