Smallpox Epidemic in Mexico (1520): Disease and the Conquest

The smallpox epidemic of 1520-1521 was the first great outbreak of a European disease on the Mexican mainland. Brought from the Caribbean by a Spanish expedition in 1520, it spread through central Mexico within months, killing a large share of the population of Tenochtitlan and its neighbours, including the Mexica ruler Cuitláhuac. Coming between the Spaniards’ expulsion from the Aztec capital and their return to besiege it, the epidemic played a major part in the Spanish conquest of the Aztec Empire.

Background: a disease new to the Americas

Smallpox is caused by the variola virus and spreads from person to person through the air and through contact. It had been present in Europe, Asia and Africa for many centuries, so most adults there had either survived it in childhood or been exposed to it. The Americas had never known it. When it arrived, it struck an entire population with no acquired immunity.

After Columbus’s voyages, smallpox was among many diseases that crossed the Atlantic in what historians call the Columbian Exchange. It reached the Spanish colony of Hispaniola in late 1518, where it killed many of the already shrinking Taíno population, and spread to Cuba and Puerto Rico.

Arrival in Mexico

In April 1520 a large Spanish force under Pánfilo de Narváez landed on the Gulf coast of Mexico, sent by the governor of Cuba to arrest Hernán Cortés. Several early Spanish chroniclers state that one man in Narváez’s company, an enslaved African often named as Francisco de Eguía, was sick with smallpox. The disease is said to have spread first at Cempoala, the Totonac town where Narváez’s men were quartered.

Smallpox has an incubation period of about 10 to 14 days, during which an infected person shows no symptoms, followed by fever and then a spreading rash. Patients are most contagious in the first week of the rash. In crowded towns and households, a single case could spread rapidly to a whole community.

Whether one man alone brought the infection cannot be confirmed, but there is no doubt that smallpox reached the mainland with this expedition. From the Gulf coast it spread along trade and travel routes into the highlands during the summer and autumn of 1520.

The epidemic in Tenochtitlan

By the time smallpox reached the Valley of Mexico, the Spaniards had been driven out of Tenochtitlan in La Noche Triste at the end of June 1520. The Mexica account preserved in Book 12 of the Florentine Codex, compiled under the Franciscan friar Bernardino de Sahagún from Nahua testimony, says the disease began around the month of Tepeilhuitl (roughly October) and raged for about 60 days.

The Nahua witnesses described sores spreading over the face, chest and whole body. The sick lay on their mats unable to move or turn over, and many died. The codex also records that many people died of hunger, because so many were ill at once that no one was left to cook or care for them. Those who survived were often scarred or blinded. The Mexica called the disease hueyzahuatl, the “great rash”.

The death of Cuitláhuac

The most important victim was Cuitláhuac, brother of Moctezuma II, who had become huey tlatoani (great ruler) in mid-1520 and led the expulsion of the Spaniards. He died of smallpox in late November or early December 1520 after a reign of about 80 days. Many other nobles, priests and experienced war leaders also died, as did rulers in other cities, including Maxixcatzin, one of the four lords of Tlaxcala and a key Spanish ally.

The Mexica chose Cuauhtémoc, a young cousin of Moctezuma, as the next ruler early in 1521. He inherited a city weakened by disease, losses in war and the disruption of food supplies.

How the epidemic shaped the conquest

Historians agree that smallpox affected the course of the conquest, but they disagree on how much weight to give it. Its effects included:

• Loss of leadership: The deaths of Cuitláhuac and many senior commanders came at a critical moment, before the Mexica could organise a lasting coalition against the Spaniards.
• Fewer defenders: The deaths of large numbers of men and women reduced the city’s ability to fight, farm and supply itself during the siege of 1521.
• Social disruption: The epidemic interrupted farming, trade and tribute, and many communities were simply overwhelmed.
• Unequal impact: Spaniards who had survived smallpox in childhood were largely immune, which some Indigenous observers interpreted as a sign of divine favour towards the newcomers.

Some historians, such as Alfred W. Crosby, have argued that smallpox was perhaps the most important single factor in the Spanish victory. Others, including Ross Hassig and Matthew Restall, emphasise the political choices of Indigenous states and the scale of the war fought by them, warning against explaining the conquest by disease alone.

At the same time, the Spaniards’ Indigenous allies suffered from the disease too, and the siege of Tenochtitlan from May to August 1521 was won through hard fighting, blockade and the support of tens of thousands of allied warriors.

Death toll

There is no reliable count of deaths. Pre-conquest population estimates for central Mexico are themselves contested, ranging from about 5 million to more than 25 million. Many historians estimate that between about a quarter and a half of the population of the affected regions died in the 1520 epidemic, but these figures rest on limited evidence.

Some Nahua annals later remembered the year of the epidemic by its sickness. Colonial pictorial histories show figures covered in spots, and Indigenous writers looked back on the disease as one of the great calamities that marked the end of the old world.

Later epidemics

Smallpox was only the beginning. Measles followed in 1531, and the epidemics known as cocoliztli, in 1545-1548 and 1576-1580, killed millions more. By around 1600 the Indigenous population of central Mexico had fallen to a small fraction of its size in 1519, one of the worst demographic disasters in recorded history.

Key people

• Cuitláhuac (died 1520): Mexica ruler who led the expulsion of the Spaniards and died of smallpox.
• Francisco de Eguía: Enslaved African in Narváez’s expedition whom early accounts name as the first person to carry the disease to Mexico.
• Pánfilo de Narváez (c. 1470s-1528): Commander of the expedition that brought the disease to the mainland.
• Maxixcatzin (died 1520): Lord of Ocotelolco in Tlaxcala and Spanish ally, who also died in the epidemic.

Timeline

• 1518, December: Smallpox breaks out on Hispaniola.
• 1520, April: Narváez’s expedition lands on the Gulf coast, carrying the disease.
• 1520, 30 June - 1 July: The Spaniards are driven from Tenochtitlan.
• 1520, autumn: Smallpox spreads through the Valley of Mexico.
• 1520, late November or early December: Cuitláhuac dies of smallpox.
• 1521, early: Cuauhtémoc becomes ruler of Tenochtitlan.
• 1521, 13 August: Tenochtitlan falls after a siege of nearly three months.

Why it matters

The epidemic of 1520 marked the start of a demographic catastrophe that transformed Mexico and the wider Americas. It shows how disease, as much as war and politics, shaped the encounter between Europe and the Americas, a story that only ended with the eradication of smallpox in the 20th century.