While Cortés was fighting Narvaez, Alvarado imprisoned two important leaders and killed several others. The tensions exploded when Alvarado ordered a massacre during the great Aztec spring festival of Huizilopochtli. Cortés returned on June 25,1520 and by June 30 the situation was desperate. The causeways were cut, the bridges taken away, and the net closed. The Spanish had no food supplies and there was an acute shortage of drinking water. Cortés forced Montezuma to try and pacify to people from the rooftop, but the emperor was forced to retreat under a hail of stones and arrows.

The Spanish later claimed that Montezuma was wounded and died of his injuries. But, hurt or not, when he was taken back to the palace, it seems clear that the "great speaker" was now understood by Cortés to have lost all his power, and was, therefore, of no further use to the Spanish. Nor were the other nobles.

News of the killing of Montezuma and the other great lords spread, and soon there was an uproar in the city. The Spaniards tried to flee unnoticed, but they were caught. A call went out and canoes began to close in on all sides. The Spanish column tried to press forward, and in the confusion, hundreds of men fell into the canal.

More than 600 Spanish conquistadors were killed (some estimates ran to over 1,000), many no doubt weighed down by the gold they were carrying; several thousand Tlaxcalans were probably lost, too. Cortés retreated in a wide circle through the north of the valley and over the mountains back to Tlaxcala. The elemental horror of that night was never forgotten. It is still called "the night of tears" (noche triste).