a painting showing Hernán Cortés at the gates of the capital of the Aztec Empire

Guns, germs, and horses brought Cortés victory over the mighty Aztec empire

The Aztec outnumbered the Spanish, but that didn't stop Hernán Cortés from seizing Tenochtitlan, the Aztec capital, in 1521.

This 18th-century oil painting, part of the Conquest of Mexico series at the Library of Congress, shows Hernán Cortés poised at the gates of the capital of the Aztec Empire.

After the expedition led by Vasco Núñez de Balboa who crossed Central America to reach the Pacific in 1513, Europeans began to see the full economic potential of this "New World." At first, colonization by the burgeoning new world power, Spain, was centered on the islands of the Caribbean, with little contact with the complex, indigenous civilizations on the mainland.

It was not long, however, before the lure of wealth spurred Spain’s adventurers beyond exploration and into a phase of conquest that would lay the foundations of the modern world. Whole swaths of the Americas rapidly fell to the Spanish crown, a transformation begun by the ruthless conqueror of the Aztec Empire, Hernán Cortés. (See also: New clues to the lost fleet of Cortés .)

Cortés beginnings

Like other conquistadores of the early 16th century, Cortés had already gained considerable experience by living in the New World before embarking on his exploits. Born to modest lower nobility in the Spanish city of Medellín in 1485, Cortés stood out at an early age for his intelligence and his restless spirit of adventure inspired by the recent voyages of Christopher Columbus.

In 1504, Cortés left Spain for the island of Hispaniola (today, home to the Dominican Republic and Haiti), where he rose through the ranks of the fledgling colonial administration. In 1511 he joined an expedition to conquer Cuba and was appointed secretary to the island's first colonial governor, Diego Velázquez.

During these years, Cortés developed the skills that would stand him in good stead in his short, turbulent career as a conquistador. He gained valuable insights into the organization of the islands’ indigenous peoples and proved an adept arbiter in the continual squabbles that broke out among the Spaniards, forever vying to enlarge their estates or snag lucrative administrative positions.

In 1518 Velázquez appointed his secretary to lead an expedition to Mexico. Cortés—as Velázquez was to discover to his cost—was set on becoming a leader rather than a loyal follower. He set off for the coast of the Yucatán Peninsula in February 1519 with 11 ships, about 100 sailors, 500 soldiers, and 16 horses. Over the following months Cortés would take matters into his own hands, disobey the governor’s orders, and turn what had been intended to be an exploratory mission into a historic military conquest.

Aztec introductions

To the Aztec, 1519 was a year that began with their empire as the uncontested power in the region. Its capital city, Tenochtitlan, ruled 400 to 500 small states with a total population of five to six million. The fortunes of the kingdom of Moctezuma, however, were doomed to a swift and spectacular decline once Cortés and his men disembarked on the Mexican coast. (See also: Rare Aztec Map Reveals a Glimpse of Life in 1500s Mexico.)

Having rapidly imposed control over the indigenous population in the coastal region, Cortés was given 20 slaves by a local chieftain. One of them, a young woman, could speak several local languages and soon learned Spanish too. Her linguistic skills would prove crucial to Cortés’s invasion plans, and she became his interpreter as well as his concubine. She soon came to be known as Malinche, or Doña Marina. The conquistador had a son with her, Martín, who is often regarded as the first ever mestizo—a person of mixed European and American Indian ancestry. (See also: Call the Aztec midwife: Childbirth in the 16th century.)

The news of the foreigners’ arrival soon reached the Aztec emperor, Moctezuma, in Tenochtitlan. To appease the Spaniards, he sent envoys and gifts to Cortés, but he only succeeded in inflaming Cortés’s desires for more Aztec riches. Cortés once described the land near Veracruz, the city he founded on the coast of the Gulf of Mexico, as rich as the mythical land where King Solomon obtained his gold. As a mark of his ruthlessness, and to quash any misgivings his crew may have had in disobeying the orders of Governor Velázquez, Cortés ordered the destruction of the fleet he had sailed with from Cuba. There was now no turning back.

Cortés had a talent for observing and manipulating local political rivalries. On the way to Tenochtitlan, the Spaniards gained the support of the Totonac peoples from the city of Cempoala, who hoped to be freed from the Aztec yoke. Following a military victory over another native people, the Tlaxcaltec, Cortés incorporated more warriors into his army. Knowledge of the divisions among different native peoples, and an unerring ability to exploit them, was central to Cortés’s strategy.

The Aztec had allies too, however, and Cortés was especially belligerent toward them. The holy city of Cholula, which joined with Moctezuma in an attempt to stall the Spaniards, was sacked for two days at Cortés’s command. After a grueling battle lasting more than five hours, as many as 6,000 of its people were killed. Cortés’s forces seemed invincible. In the face of their unstoppable advance, Moctezuma stalled for time, allowing the Spaniards and their allies to enter Tenochtitlan unopposed in November 1519.

Fighting on two fronts

Fear gripped the huge Aztec capital on Cortés’s entry, the chroniclers wrote: Its 250,000 inhabitants put up no resistance to Cortés’s small force of a few hundred men and 1,000 Tlaxcaltec allies. At first Moctezuma formally received Cortés. Seeing the value of the emperor as a captive, Cortés seized him and guaranteed his power over the city.

Establishing a pattern that would recur throughout his career, Cortés soon found himself as much at threat from his own compatriots as from the peoples he was trying to subdue. At the beginning of 1520 he was forced to leave Tenochtitlan to deal with a punitive expedition sent from Cuba by the enraged Diego Velázquez. In his absence, Cortés left Tenochtitlan under the command of Pedro de Alvarado and a garrison of 80 Spaniards.

The hotheaded Alvarado lacked Cortes’s skill and diplomacy. During Cortes’s absence, Alvarado’s execution of many Aztec chiefs enraged the people. After defeating Velázquez’s forces, Cortés returned to Tenochtitlan on June 24, 1520, to find the city in revolt against his proxy. For several days, the Spaniards vainly used Moctezuma in an attempt to calm tempers, but his people pelted the puppet king with stones. Moctezuma died a few days later, but his successors would fare no better than he did.

On June 30, 1520, the Spanish fled the city under fire, suffering hundreds of casualties. Some Spaniards died by drowning in the surrounding marshes, weighed down by the vast amounts of treasure they were trying to carry off. The event would come to be known as the Night of Sorrows.

A smallpox epidemic prevented the Aztec forces from finishing off Cortés’s defeated and demoralized army. The outbreak weakened the Aztec while giving Cortés time to regroup. Spain would win the Battle of Otumba a few days later. Skillful deployment of cavalry against the elite Aztec jaguar and eagle warriors carried the day for the Europeans and their allies.“Our only security, apart from God,”Cortés wrote,“is our horses.”

Victory allowed the Spaniards to rejoin with their Tlaxcaltec allies and launch the recapture of Tenochtitlan. Waves of attacks were launched on settlements near the Aztec capital. Any resistance was brutally crushed: Many indigenous enemies were captured as slaves and some were even branded following their capture. The sacking also allowed the Spaniards to build up their large personal retinues, taking captives to use as servants and slaves, and kidnapping others for exchanges and ransoms. Growing in number to roughly 3,000 people, this group of captives vastly outnumbered the fighting Spaniards.

Fall of the Aztec

For an assault on a city the size of Tenochtitlan, the number of Spanish troops seemed paltry—just under 1,000 soldiers, including harquebusiers, infantry, and cavalry. However, Cortés knew that his superior weaponry, coupled with the additional 50,000 warriors provided by his indigenous allies, would conquer the city, which was already weakened from starvation and thirst. In May 1521 the Spaniards had cut off the city’s water supply by taking control of the Chapultepec aqueduct.

Even so, the siege of Tenochtitlan was not a given. During fighting in July 1521, the Aztec held strong, even capturing Cortés himself. Wounded in one leg, the Spanish leader was ultimately rescued by his captains. During this setback for the conquistador, the Aztec warriors managed to regain lost ground and rebuild the city’s fortifications, pushing the Spanish onto the defensive for nearly three weeks. Cortés ordered the marshland to be filled with rubble for a final assault. Finally, on August 13, 1521, the city fell.

“Not a single stone remained left to burn and destroy,” one witness wrote. The loss of human life was staggering, both in absolute figures and in its disproportionality. During the siege, around 100 Spaniards lost their lives compared to as many as 100,000 Aztec.

The conquest of Tenochtitlan and the subsequent consolidation of Spanish domination over the former Aztec Empire was the first major possession in what became the Spanish Empire. This vast territory would reach its greatest extent in the 18th century, with territory throughout North and South America.

Cortés’s triumph would be short-lived. In just a few years, he would lose many of his lands in the New World. Despite being made a marquis years later, the Conqueror of Mexico did not have a glorious end. In 1547, at the age of 62, he died in a village near Sevilla, Spain, embroiled in lawsuits and his health broken by a series of disastrous expeditions. Decades of rapid expansion in the Americas seemed to have eclipsed his own exploits, and few bells tolled for the man whose ruthlessness and cunning transformed the Americas.

A specialist in the Spanish Empire, Hernández is professor of Modern History at the Autonomous University of Barcelona, Spain.

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