The Aztecs were for centuries a poor nomadic tribe eking out a living in northern Mexico, but in the 12th century they relocated to central Mexico. By the time of the arrival of Spanish conquistador Hernán Cortés in 1519, the Aztecs dominated central Mexico and as far south as present-day Guatemala; their capital had swollen to more than 100,000 people.Through the processes of absorption and conquest, the Aztecs created a complex society that featured advanced agriculture, mathematics, astronomy and art. They were not the great innovators that their predecessors had been and borrowed heavily from the Mayans in particular. The Spanish conquerors discovered some 100,000 human skulls in a single depository.The question of how such a powerful empire collapsed so quickly and completely before the Spanish onslaught remains a topic of considerable debate. By the time the Spanish arrived, many of the Aztecs were emotionally spent.