Although some indigenous peoples of the Americas were traditionally hunter-gatherers—and many, especially in the Amazon basin, still are—many groups practiced aquaculture and agriculture. The impact of their agricultural endowment to the world is a testament to their time and work in reshaping and cultivating the flora indigenous to the Americas. Although some societies depended heavily on agriculture, others practiced a mix of farming, hunting and gathering. In some regions the indigenous peoples created monumental architecture, large-scale organized cities, city-states, chiefdoms, states, kingdoms and empires. Among these are the Aztec, Inca and Maya states that until the 16th century were among the most politically and socially advanced nations in the world. They had a vast knowledge of engineering, architecture, mathematics, astronomy, writing, physics, medicine, planting and irrigation, geology, mining, sculpture and goldsmithing.