What role did trade play in the Aztec empire?

There are two roles, both important and quite different.

The Aztec marketplaces are legendary for at one time providing some of the most exotic plants, meats, vegetables, fruits, medicinal plants and herbs, feathers, pelts, stones, dyes, art, wares, fabrics, etc. For example, Tenochititlan (Mexico City) was supplied with fresh fish from both coasts. The Aztec marketplace has survived the centuries and become the popular "mercados" and weekly "tianguis".

Trade is believed to have been an essential part to the greatness of the Aztec culture. The Long-Distant Merchants (Pochteca) were instrumental to bring back information about other regions, size of towns and tribes as well as maps of the best routes to reaching all these far way places. The Pochteca brought back information on what goods the Aztec could benefit from, and more importantly the strength and weaknesses of the other tribes. That made the Pochteca an essential instrument to the height of the Aztec empire. It is recorded in history the Pochteca did trading as far as northern New Mexico (many believe it was much further to the north), and far into South America. The central American country of Nicaragua was under the ruling of the Aztec, its original name Nikan Anahuak roughly transalates "This far reaches Anahuak"

Due to its important role in the expansion of its empire, the Pochteca had a high place within society. The only way to become a pochteca, was to be born into such class.