June 30, 1520: A fierce battle breaks out in the capital of a great empire. The Aztec ruler, Montezuma II, is found dead. Aztec warriors chase Spanish invaders from Tenochtitlán (tay-nawch-teet-LAHN), their biggest city. 

The fleeing Spanish carry bars of gold and other treasures they stole from the Aztecs. Some soldiers drop the gold as they try to escape through the city’s canals. Weighed down by the loot, others fall into the water and drown. To the Spanish, that night becomes known as La Noche Triste, or “the Sad Night.” 

Now, nearly 500 years later, researchers have determined that a gold bar discovered in Mexico was part of the Aztec treasure lost on that historic night.

The Aztecs were a wandering people who settled in what is now central Mexico beginning in the late 13th century. They built a powerful civilization that thrived for about 200 years.

“There were several million Aztecs,” says Michael Smith, an archaeology professor at Arizona State University. “They had a large, complex society.”

The Aztecs built vast temples and palaces, developed advanced methods of farming, and created a writing system using symbols. Aztec children went to school and studied history, art, and music. 

Tenochtitlán was the center of the empire. It was set on an island in a lake and had canals for streets. 

In 1519, the Aztec Empire was at the peak of its power when conquistadors, or conquerors from Spain, arrived. They were led by Hernán Cortés (ehr-NAN kor-TEZ). Montezuma II was uncertain about the visitors, but he invited them to stay in his palace. The Spaniards weren’t very good guests, however. For one thing, they began stealing Aztec jewelry. 

“They wanted gold that they could carry back to Spain,” says Smith. “They had metalworkers melt down a lot of the jewelry and form it into gold bars.”

Soon the relationship grew sour, and the Spanish took Montezuma II prisoner. Historians aren’t sure exactly who killed him on June 30, 1520, but they agree that his death was the beginning of the end of the Aztec Empire. After fleeing Tenochtitlán that night, Cortés and his army returned about a year later. They soon conquered the Aztecs and established a new colony.