In the days that followed, Cortés and his men marvelled at the treasures of Tenochtitlán - the strange foods, the "wondrous artefacts" - and were horrified by the Aztec religious rites of human sacrifice.

Cortés was also uneasy. The Spaniards were vastly outnumbered and he feared that Montezuma could be plotting to destroy them. Thus, on November 16, Cortés detained Montezuma. He placed the Aztec emperor under house arrest and attempted to rule the Aztecs through the emperor. However, the power of the Aztec king was dwindling in the eyes of his people. The Aztecs grew ever more resentful of the Spaniards' attacks on their religion and their relentless demands for gold.

When resistance broke out among the people of a powerful lakeside ruler, Cortés held a ceremony to formalize Montezuma's submission to the King of Spain. He next installed Christian images on the great pyramid, and set in motion the first attempts to destroy the Mexican idols. Still trying to be reasonable, Montezuma suggested an astonishing compromise: the placing of his gods on one side, the Christians on the other.

Cortés was scrambling to subdue the increasingly agitated Aztecs when he received news that a large Spanish force had arrived. It was an arrest party sent by the governor of Cuba. Cortés left Tenochtitlán in the hands of Alvarado. And, with Montezuma in chains, he rushed out to meet the forces of Panphilo de Narvaez. Cortés surprised Narvaez on the coast at Zempoala, attacking him at night. For Cortés, the outcome was better than he could have hoped. Thanks to Narvaez, defeated, his surviving troops reinforced Cortés who returned to Tenochtitlán in formidable numbers.