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Exploring the Darker Side of Everything

The Century that Devastated Mexico

There are periods of bad luck and then there was the 16th Century in the area that broadly encompasses present-day Mexico. If we want to be really specific – and why the hell not – today we’re talking about a period between 1517 AD and around 1580 AD. Little more than 60 years, but they were 6 decades that forever changed the local demographic and social structure.

I’m going to say from the outset, there’s absolutely nothing cheery about this story of invasion, war, conquest, virtual enslavement and not one, not two, but three catastrophic outbreaks that completely obliterated the native population. What occurred in the region remains one of the most dramatic demographic collapses ever seen and it completely reshaped society. 

If all of that wasn’t bad enough, this is also a story of a mystery disease that tore through New Spain on several occasions and which still hasn’t been completely explained. The cocoliztli epidemic remains an enigma, although there are several modern theories that we’ll go into later in the video. But what’s clear is the trail of utter devastation it left. Between 5 and 15 million died in the first outbreak alone, a figure that added up to roughly 80% of the population at the time. 

Exact numbers are difficult to ascertain, but across the whole of the 16th Century, between 60 and 70% of the ingenious society was wiped out. When the Spanish arrived in 1517, the local population was anywhere between 15 and 30 million people, but by the end of the century, that had collapsed to just 2 million, a demographic catastrophe with few equals. 

Early Americas  

This part of the world had seen seemingly near apocalyptical events before and like the cocoliztli epidemics, they remain somewhat mysterious. Around 250 AD, the Maya civilization was approaching its peak, and what a peak it was. The cities of Palenque, Copán, Tikal, Toniná, Yaxchilán, Banampak and of course Chichen Itza, which rose to prominence a little later, were beyond spectacular, and easily rivalled other great ancient cities at the time.  

But something happened to the Maya civilization – or most likely, a series of things. One by one, the great cities were abandoned as people began to move north. Exactly why remains a mystery, but most historians agree it was probably down to a combination of overpopulation, environmental degradation, warfare, shifting trade routes and extended drought. 

By 900 AD, the Classic Maya civilization had all but collapsed, bringing to an end the greatest ancient civilization of the Americas.  

The Aztecs   

But the collapse of one great civilisation would eventually give rise to another with the Aztec Empire gaining momentum from the early years of the 13th Century. Groups that probably began as nomadic hunters grew into a formidable power that was able to dominate Mexico for almost two centuries.

The Triple Alliance, a confederation of three city-states, Mexico-Tenochtitlan, Tetzcoco, and Tlacopan, dominated the region after banding together in 1430. Tenochtitlan, which now forms the historic centre of Mexico City, at its peak was one of the largest cities in the world with more than 140,000 inhabitants. By the early 16th Century, the Aztec Empire included around 500 separate small states and perhaps as many as 6 million people. 

And this was quite an empire with thriving commerce, beautiful art, science, and a highly structured society. It’s probably fair to think that at the dawn of the new century, things were looking rather rosy for the Aztec leaders. 

The Conquistadors

But of course, this sense of confidence started to come crashing down on 1st January 1517, when F. Hernández de Córdoba landed on the coast of the Yucatan. Just two years later, the first major attempt to colonize the area began as the Spaniards sent Hernan Cortes, along with 500 men, to conquer the Aztec Empire. 

And this conquest went at quite a pace. The Spanish managed to align themselves with the Tlaxcalteca people – after the two had fought viscously beforehand that is – and were eventually able to steamroll all before them. After entering Tenochtitlan initially as welcomed guests, the Spaniards and their allies took Emperor Motecuzoma and many of his nobles hostage and a bizarre situation began where the Emperor technically still ruled while under virtual house arrest in his own city.

A series of savage massacres took place as the Spanish began to show their true colours and Emperor Motecuzoma died in mysterious circumstances. With things spiralling out of control, the Spanish and their allies tried to make a sneaky escape under the cover of darkness – in what has come to be known as the ‘Sad Night’ – but were caught and had to fight their way out with a heavy loss of life.  

But of course, they weren’t finished. After retreating, Cortes managed to persuade other small states to join his cause, and eventually returned to Tenochtitlan with roughly 100,000 men. The siege of this great city lasted several months, but the invading band of Spanish and disenchanted locals entered Tenochtitlan on 13th August 1521, after hellish fighting that killed as many as 250,000, effectively ending the Aztec rule. 


But the city they entered was already radically different. Not only had it been largely destroyed through fighting, but its population had also already crumbled. The Spanish not only brought guns that were able to overwhelm the greater numbers of Aztec warriors, but they also brought a disease that ravaged the local population. 

In 1520, smallpox began spreading from the sparsely populated coastal regions inland. When it arrived in Tenochtitlan, the results were horrific, and remember the Aztecs were also fighting for their lives against the Conquistadors. An estimated 40% of the city’s population died as a result of smallpox in a single year, with anywhere between 5 and 8 million dying across Mexico. The tragic irony was that it affected the Spanish considerably less than the indigenous people. 

It’s difficult to describe the living nightmare that many found themselves in around this time, caught between the near-genocidal tactics of the Spanish and a mystery disease they had never experienced before, and that was now running wild. And sadly, this was just the start of a period that would see one of the fastest falls in demographic numbers in world history. 

Spanish Rule

You probably don’t need me to tell you that life under Spanish rule was bad from the very get-go. As a way of rewarding soldiers who had participated, a forced labour system, known as the Encomienda System, which had its roots in a preexisting system that the Aztecs had used, was introduced across the region. Essentially this meant that local people were forced to pay a tribute to their specific conquistador and more often than not this came with brutal work that was little more than slavery. 

Silver mines began to offer a glimpse of the fabulous wealth that the Spanish would gradually milk from Mexico and the practice of slavery continued until 1542 when it was formally outlawed. Now again, just for the sake of balance, slavery was far from an alien concept to the Aztecs who had used it well before the arrival of the Spanish, but things were ramped up significantly.   

Between 1521 and 1545, the Spanish gradually expanded their sphere of influence, while attempting to stamp their own ideas regarding education and religion on the indigenous people. This shaky, fractious new society was slowly emerging, when hell descended.   

First Outbreak

The first recorded mention of what we now refer to as Cocoliztli came in 1545, but a total of 12 epidemics have been loosely associated with the mystery disease – the most significant coming in 1545, 1576, 1736, and 1813, with the 1520 smallpox epidemic is also sometimes erroneously attributed to it. 

When the first cocoliztli epidemic erupted in 1545 nobody had ever seen anything like it – neither the indigenous people nor the ruling Spaniards. With our modern knowledge, cocoliztli is probably best compared to Ebola, both because of its symptoms and terrifying results. It was also rapid, raging through its victims in a matter of three to five days, which either left the patient a withering wreck or dead. This short time was filled with a horror that thankfully most of us will never need to experience. 

It began with a high fever, vertigo, severe headache, insatiable thirst, red eyes and a weak pulse. Next, because of jaundice, patients turned a sickly yellow while becoming increasingly anxious, demented and restless. After this, hard nodules appeared behind the ears that could grow so large they would even spread across the face, which could be painfully burst and drained of the pus within. And just as an act of warning for those who might already be feeling a little queasy, I’m afraid we’ve only just started. 

This was usually accompanied by intense chest and abdominal pain, along with dysentery, and ulcers on lips and genitals. Blood then began to seep from every imaginable place it can – and I do really mean every – while the urine typically turned dark – a sign that the end was near.  

This being 1545, medical know-how was still rudimentary, to say the least, and even so, the rapid spread completely overwhelmed any hope of medical attention. A small number of autopsies were performed that usually reported a very enlarged and hard liver, lung haemorrhage and splenomegaly – an abnormal enlargement of the spleen. Interestingly, it was highlighted at the time that none of the doctors performing the autopsies with their bare hands came down with the illness. 

The disease ransacked the area in a way few diseases have done throughout history. In case you’re interested – and I’m sure you are – the cocoliztli epidemic currently ranks 6th in the worst epidemics or pandemics in human history. The third plague pandemic between 1855 and 1960 killed an estimated 12 to 15 million people, HIV, which exploded in the early 1980s has killed over 35 million and is still ongoing, the Plague of Justinian killed anywhere between 15 million and 100 million people between 541 and 549 AD and the Spanish Flu was responsible for up to 100 million deaths between 1918 and 1920. 

And lastly, we come to the top dog, the murderous overlord of them all. The Black Death, which ravaged Europe, Asia and North Africa between 1346 and 1353 AD, was responsible for up to 200 million deaths, with Europe losing between 20 and 60% of its population. In comparison, the cocoliztli epidemic which killed between 5 and 15 million sounds fairly small fry, but 15 million is still the entire population of Zimbabwe today and this was not spread evenly around the world. This was a harrowing epidemic that focused almost entirely on a very specific area in Central America.         

But as I mentioned earlier, it certainly didn’t affect everybody the same. While the Spanish had never seen anything like cocoliztli, their bodies fared substantially better than the native population. Cocoliztli acted like a sledgehammer to the indigenous people, while the newcomers were minimally affected. Even when they did catch the disease, it often had a benign course. To make things even worse for the local people, those who survived often fell into relapse, and with the body severely weakened already, a second survival was rare.     


A few decades of relative calm followed the hellish appearance of cocoliztli in 1545. I say calm, but with such horrific losses, there must have been an air of utter desperation. Exact figures are difficult to come by regarding the first outbreak, but a census conducted in 1570 and another 1580 painted a horrifying picture – because between these two counts, cocoliztli returned.

Unlike the first outbreak, which was first recorded near the coast, the second cocoliztli outbreak appeared in the valleys of central Mexico, before reaching north into Sonora and south into the Yucatan Peninsula and what is present-day Guatemala. By April 1576, the first cases were reported within the valleys surrounding Tenochtitlan. During the summer months, the disease crept closer to the most heavily populated area in the region, but unlike 1545, cases and deaths remained mysteriously low. 

But that all changed when the rainy season reached its crescendo in September 1576 and cases exploded in every region. The peak of this outbreak lasted from September until March 1577, and it can be difficult to describe just how shocking this was. In relatively isolated rural towns it wasn’t unheard of for 20 to 40 people to die each day, while in larger towns, hundreds perished every 24 hours as cocoliztli raged out of control. 

It wasn’t until October 1577 that cases began to fall, and while numbers see-sawed over the next year, the outbreak was finally declared over in December 1578. But not so fast Mexico. Cocoliztli returned once again during the rainy season in 1579, though mortality rates were significantly lower than in previous cases. 

As I said, two censuses were conducted around this time, one before the outbreak and one after, and reveal both the true devastation of the cocoliztli outbreak and the extent of the mortality differences between the indigenous people and the Spanish.  

Amazingly, the Spanish population saw many sizable increases in population between 1570 and 1580. Mexico City for example had had a 33% increase in its Spanish population by 1580, while the city of Panuco, located in present-day Veracruz saw an astonishing 3746% increase. 

On the other hand, the Native population experienced dramatic falls during this period. In Panuco, indigenous numbers fell by 76% and in Mexico City by 25%. On average, most areas saw a drop of between 40% and 60%, while in Valles, a city north of Mexico City, the native population suffered an unimaginable 96% decrease in just a decade. 

Roughly speaking, highland areas did worse than lowland areas, but rural and urban locations appeared to be both equally affected. 


Our understanding of this horrific disease has barely changed since 1576, though recent findings have begun to unravel its potential roots. But before we dive into DNA and theories surrounding the origin of cocoliztli, let’s start with the ecological factors at play. 

The 16th Century not only brought smallpox and cocoliztli to Mexico, but it was also the setting of one of the most devastating droughts the region has ever seen. The Megadrought that this area experienced during the 16th Century profoundly affected ecosystems and societies that stretched from Southern Mexico into what are now the southwestern states of the U.S. It’s a little difficult to get a clear idea of just how damaging it was because of the raging epidemics but it’s clear it added another layer to the horror that the region experienced during the 16th Century. 

And I’m afraid it gets worse. By some excruciatingly cruel twist of fate, the cocoliztli outbreaks almost exactly coincided with abundant rainfall during specific rainy seasons. So it seems the option was either drought or heavy rain with cocoliztli. 

Historians have debated the origins of cocoliztli for centuries now, with yellow fever, plague, leptospirosis, hepatitis, malaria, dengue, hantavirus, arenavirus and bartonellosis all considered at some point. Frustratingly, cocoliztli shares similarities with many of these, but this may simply reflect common physiopathological processes. 

But perhaps there has been a breakthrough in the last few years. Tests done on the teeth of skeletons found in Mexico have revealed a rare form of salmonella, but only in those whose deaths occurred after the arrival of the Spanish. Skeletons whose death predated the arrival of the Conquistadors did not show the same disease. 

But most agree that cocoliztli bears little resemblance to salmonella outbreaks that we see today. It’s possible that this was a rare variation but it’s unlikely that it could have caused devastation on this kind of level alone. When we consider that the Spanish almost exclusively escaped the horrors of cocoliztli we have to assume some kind of immunity brought over from Europe, but may also have been linked with the malnutrition and generally terrible conditions that most indigenous people found themselves in after the arrival of the Spanish. When we add in the disruptions in food supplies, famine, changes in the concentrations of populations, and relocation of people, we have a perfect storm that absolutely devastated Mexico.  

A Century of Hell

That wasn’t the last of cocoliztli, with sporadic flare-ups continuing until 1813 – the last recorded outbreak. But these were nothing compared to the two major outbreaks during the 16th Century. It is however important to point out that it was always the poor who suffered the most during these smaller outbreaks, as Mexico’s population experienced radical change as Spanish blood began to dominate the area. 

As the 16th Century drew to a close, it’s difficult to imagine a more devastating hundred years anywhere in the world. The native population had been first defeated by the Spanish, then essentially enslaved, and finally almost exterminated by a series of diseases that pushed a society to the verge of extinction. 

It would take 350 years until the population in Mexico recovered to where it had been in 1544, while the native way of life all but collapsed. Demographically, the country was forever altered as the Spanish culture dominated and traditions that had survived for centuries disappeared. With one of the sharpest drops in human population ever recorded, this was the horrifying century that razed Mexico to the ground. 

One of history’s worst epidemics may have been caused by a common microbe | Science | AAAS (sciencemag.org)

Megadrought and Megadeath in 16th Century Mexico (nih.gov)

When half of the population died: the epidemic of hemorrhagic fevers of 1576 in Mexico | FEMS Microbiology Letters | Oxford Academic (oup.com)

Deadly Aztec Epidemic “Cocoliztli” Linked to Salmonella (nationalgeographic.com)

A New Clue to the 1545 Cocoliztli Epidemic in Mexico – The Atlantic

500 years later, scientists discover what probably killed the Aztecs | Mexico | The Guardian

This is Why the Maya Abandoned Their Cities – HISTORY

Mexico History and Timeline Overview (ducksters.com)

Spanish conquest of the Aztec Empire – Wikipedia500 Years Later, The Spanish Conquest Of Mexico Is Still Being Debated : NPR

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