Smallpox Sweeps Through Tenochtitlan
A disease no one in the Americas had immunity to kills faster than any army, striking the capital within months of the Spanish retreat
Quick facts
- Outbreak
- September-December 1520
- Likely source
- Member of Narvaez's Spanish force
- Estimated deaths, Mesoamerica-wide
- 5-8 million (per Dumbarton Oaks)
- Notable death
- Cuitlahuac, Aztec ruler, after c. 80 days
What happened
Smallpox broke out in Tenochtitlan in the months after the Noche Triste, most likely carried by a member of the rival Spanish force Cortes had defeated at Veracruz. Dumbarton Oaks Research Library's exhibit on the epidemic quotes the Florentine Codex's account from a survivor: sores erupted across the body, victims became too weak to move or even lie face down without unbearable pain, and many who did not die directly from the disease starved to death because everyone around them was too sick to provide care. In a population that had never previously encountered the virus, mortality among the infected could run as high as 100 percent depending on the strain, and Dumbarton Oaks cites estimates of five to eight million deaths across Mesoamerica during this single outbreak. The Aztec ruler Cuitlahuac, who had taken power after Moctezuma's death only weeks earlier, was among those who died of the disease, reigning for a reported 80 days before smallpox killed him too.
Why it matters
The epidemic did not conquer Tenochtitlan by itself, siege warfare and the Tlaxcalan alliance mattered enormously too, but it decapitated Aztec leadership twice in rapid succession and devastated the population and supply networks the city would need to survive the coming siege. The timing, arriving in the months between the Noche Triste and Cortes's return with reinforcements, was one of the most consequential accidents of the entire conquest.
How we know
The epidemic's course and symptoms are recorded directly in the Florentine Codex, based on testimony from Nahua survivors interviewed by Bernardino de Sahagun's informants within a generation of the outbreak, giving historians an indigenous firsthand account rather than only a Spanish one.
Sources
- Dumbarton Oaks Research Library and Collection. The Great Epidemic of 1520 · Reputable sourcedoaks.org · The domain "doaks.org" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- Dumbarton Oaks Research Library and Collection. The Great Epidemic of 1520 · Reputable sourcedoaks.org · The domain "doaks.org" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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