Following the death of Aztec emperor Moctezuma II and rising fury at Spanish occupation, Hernán Cortés's conquistadors attempted a desperate nighttime retreat from Tenochtitlan across the city's causeways. Aztec warriors, alerted to the escape, attacked the fleeing column, killing hundreds of Spaniards and thousands of their Tlaxcalan allies, along with much of the looted treasure. The rout, remembered as La Noche Triste, nearly ended Cortés's campaign before he regrouped and returned a year later to conquer the city.
By mid-1520, Cortés's occupation of the Aztec capital Tenochtitlan had grown untenable. His forces had taken Moctezuma II hostage, but the emperor's authority collapsed after Spanish soldiers massacred Aztec nobles during a religious festival, and Moctezuma died shortly afterward, either killed by his captors or by his own people, accounts differ. With the city in open revolt and the Spanish garrison besieged and starving, Cortés decided on a night escape across the causeways connecting Tenochtitlan to the mainland.
The retreat, launched around midnight, went badly from the start. Aztec sentries spotted the column and raised the alarm; warriors attacked from canoes and rooftops as the Spanish and their Tlaxcalan allies struggled across narrow causeways and makeshift bridges under a driving rain. Soldiers weighed down with looted gold drowned in the lake; estimates suggest hundreds of Spaniards and thousands of allied warriors died in a single catastrophic night.
Cortés himself survived, reportedly weeping beneath a tree afterward, an event later commemorated as 'the tree of the sad night.' Rather than ending the conquest, the disaster only delayed it. Cortés retreated to Tlaxcala, rebuilt his alliance and forces, and returned within a year to besiege and ultimately destroy Tenochtitlan in 1521, ending the Aztec Empire.