While Cortes was in the city, he heard that a large Spanish force had arrived on the coast to arrest him. Cortes rushed to the coast and defeated the force that had come to capture him. He convinced the defeated soldiers to join him. While he was away, his lieutenant Pedro de Avarado, attacked the Aztec in their temple celebrating their festival of Toxcatl. According to the Spanish, they were interrupting a human sacrifice. To the Aztec it was an unprovoked massacre of their noble men..
The massacre at the Temple turned the natives against the Spanish and their own king. The Spanish demanded that Montezuma speak to his people and convince them to let the Spanish leave peaceably. The Aztec people greeted their king by stoning him. He was hit by a rock and fell down. He died soon after, either as a result of the injury, or at the hands of the Spanish. On July 1, 1520, Cortes' small army left their compound, and headed for the causeway out of the city. They reached the Tiacopan causeway and were spotted by Aztec warriors. As they crossed the causeway, in what became known as the La Noche Triste, or sad night, thousands of Aztec warriors attacked them. The Spanish were weighed down by all the gold they were carrying. Over half of the Spanish soldiers died crossing the causeway to the mainland. In addition over 1,000 native allies of Cortes perished.
The Aztec were not able to enjoy their victory over Cortes, for the Spanish had left behind a gift- a disease. The disease was most likely smallpox. It devastated the Aztec population, both physically and emotionally. When Cortes returned a few months later, with a larger Spanish army, and thousand of Native American allies, they were able to overcome the larger Aztec forces. The Aztec fought to the bitter end, but the better-armed Spanish soldiers could not be fought. The city of Tenochiitlan had fallen and with that, so did the Aztec Empire.