The Fall of the Aztecs
Spanish forces overthrew the Aztec Empire in today's Mexico,
killing their king and thousands more in the initial massacre.
But the majority of Aztec deaths came from disease, which scientists
now believe was worsened by the disruption of the Aztec's
sophisticated sewage system.
The Aztec people had a sophisticated culture in central Mexico
in the 1300s to the 1500s.
Their three principal city-states formed an alliance that controlled
what is often referred to as an empire.
Their cities were filled with amazing architecture and art.
Then the Spanish arrived in the early 1500s.
In 1520 the Spanish killed the Aztec leader and many nobles and priests
celebrating a festival in the main temple of their principal city.
Over the coming days they killed thousands more.
The real slaughter came through waves of disease
in the following years.
The Spanish had brought the germs, but the diseases are now thought to
have spread further and faster because the sophisticated Aztec
drainage and sanitary system had been damaged.
Hernán Cortés described the Aztec aqueducts in 1520.
The conquistador Andres de Tapia reported, amazed,
that Montezuma bathed twice a day.
The Jesuit historian Francisco Javier Clavijer wrote that
all the Aztec people, not just their ruler, "bathed often,
and many of them every day".
The Florentine Codex, written with the assistance of Aztec
prisoners shortly after the Conquest, described Aztec soap,
deodorants, breath fresheners, and dentifrices.
Spaniards of that time cleaned their teeth with urine,
if at all.
The Moors had invaded Spain, so the Spanish people saw the
cleanliness of the Islamic invaders as a sign of their heresy,
so their own dirtiness must be a Christian virtue.
The Maya civilization had come first, rising around 2000 BCE.
They developed sophisticated art and architecture.
Historians have recently discovered that they had developed a
pressurized water distribution system.
Their mathematics included one of the earliest uses of zero,
and their complex calendar system covered vast periods of time.
They also developed a logosyllabic script,
the most advanced writing system in the Americas.
It wasn't all science and art.
Warfare was a constant feature of Maya life,
and it eventually turned destructive.
In the 800s CE the Maya political system collapsed.
The cities were mostly abandoned.
Small villages could escape the later Spanish invasion and colonial authority.
Today there are still millions of Maya-speaking people in villages,
eating the traditional diet, producing the traditional crafts,
and even following the ritual tzolk'in calendar.
The Aztec people were based in today's central Mexico.
They were made up of various ethnic groups, dominated by those who
spoke the Nahuatl language that is the source of many
place names including "Mexico" itself.
The main Aztec city was Tenochtitlán, on a cluster
of islands in Lake Texcoco.
Tenochtitlán was allied with two other city-states,
the Acolhuas of Texcoco and the Tepanecs of Tlacopan.
This Aztec Triple Alliance or Aztec Empire controlled a large area.
Mexico's flag shows the eagle, snake, and cactus of Nahuatl prophecy.
The state religion of the Nahuatl-speaking people awaited the fulfillment
of a specific prophecy: the wandering tribes would found a great city
on a spot signaled by an eagle eating a snake while perched on top of a cactus.
The Mexica tribe arrived from the north in the mid 1200s CE.
According to legend, they saw the vision of the eagle, snake, and cactus
in 1323 on a small swampy island in Lake Texcoco.
They founded what would become the imperial city of Tenochtitlán.
In 1427-1428 the Aztec Triple Alliance was formed,
and over the following century it grew to dominate central Mexico.
Today you can see ruins of Tenochtitlán at the center of Mexico City,
just off the Zócalo.
The city was centered on the ritual precinct and
the Great Pyramid of Tenochtitlán.
The pyramids, temples, and palaces were built of stone,
while houses were made of wood and turf with reed roofs.
The islands were surrounded by chinampa beds, raised plant beds
on the shallow lake bottom that provided up to seven crops per year.
Chinampas were built from layers of mud from the lake bottom
and vegetation, and were separated by narrow canals navigated by canoes.
They built a series of dams and separated the lake into areas of its
natural brackish water and fresh water coming in from streams.
Modern Mexico City is built on the old lake bed.
Its first problem is that it does not drain well,
the city is susceptible to flooding.
The second is that the soil liquifies during earthquakes
(that is, becomes fluid, not wet), intensifying their effects.
The Aztec empire was at its peak during the reign of Ahuitzotl
as Hueyi Tlatoani or supreme leader in 1486-1502 CE.
His successor was Motehcuzōma Xocoyotzin, referred to by the
Europeans as Moctezuma or Montezuma.
The Spanish Arrive
Spanish forces led by Hernandó Cortés landed on the
Gulf Coast of Mexico in 1519.
Cortés initially fought battles there against
the Confederacy of Tlaxcala, a long-time enemy of the Aztecs.
Then Cortés and the Tlaxcalans joined forces and marched inland.
The Spanish-led forces arrived at Tenochtitlán on November 8, 1519.
They moved into the capital city and made themselves at home,
becoming increasingly dangerous and unwanted over the coming seven months.
Hostilities increased until June 1520, when the Spanish killed
Motehcuzōma Xocoyotzin and many nobles and priests who
were celebrating a festival in the main temple.
The Spanish and their allies fled on July 1, now known as
La Noche Triste or the Sad Night.
Spanish forces returned in the spring of 1521,
laying siege to Tenochtitlán through the summer.
On August 13 the Spanish finished destroying the city.
A smallpox outbreak had burned through the city's population during
the siege, killing between 10% and 50% of the population.
Sanitation is Disrupted, Disease Spreads
The population of today's Mexico is estimated to have been 25 million
when the Spanish arrived in 1519.
100 years later, it had fallen to around 1 million.
Most of the deaths were caused by disease brought by the Europeans,
spread by their disruption of the Aztec public sanitation system.
Toilet with a drainage system have been around at least since 3,000 BCE
as you can see at
Skara Brae in Orkney,
off the northern coast of Scotland.
The cities of Harappa and Mohenjo-daro in the Indus river valley had
flush toilets in most homes
connecting to a common sewage disposal system as early as 2600 BCE.
The Minoans on Crete and Thera
had flushing toilets starting around 1800 BCE.
The Greeks on the
sacred island of Delos
had large-scale public plumbing in addition to private
latrines flushed by running water in the period from
900 BCE to 100 CE.
However, plumbing technology entered a long decline in Europe
starting with the collapse of the Roman Empire.
When the Spanish explorers reached the Americas,
they were astounded to find enormous cities with highly
effective waste disposal systems.
Streets in western Europe were open sewers.
Wealthy people dumped chamber pot contents out of upstairs windows.
The non-wealthy simply used the streets as their toilets.
"Good sanitation" meant getting the sewage to drain toward the middle
of the road, where it could then flow toward some point where it could dump
directly into a stream.
Most Europeans had to wait until the late 1800s to get access
to flush toilets.
The Spanish conquest collapsed the local society.
It largely ended the public sanitation system.
The Spanish relocated the local people and forced them into
new subsistence farming practices.
Aztec culture and the Nahuatl language live on today
in towns like Tepoztlán, south of Mexico City.
Legend says it's the birthplace of Quetzalcoatl.
The Spanish brought many germs for which the people of the Americas had
In some cases the diseases advanced faster than the European invaders,
so that most of the local people might be dead by the time the
Most infectious diseases leave no signs on the skeleton,
the main or only remains we have to examine today.
Historical descriptions of disease may be detailed but tend not
to be very useful.
They are distorted by inaccurate translation and cultural biases,
they date from times with very little knowledge of medicine and
none of germ theory, and sometimes they are describing historical
conditions that differ from modern cases.
The local people described the worst of the epidemics as
cocoliztli, meaning "pestilence".
The Spanish called it pujamiento de sangre or "full bloodiness".
Neither term is any help in figuring out what it really was.
The cocoliztli of 1545-1550 was one of the principal epidemics
causing the population crash of 16th century Mesoamerica.
It covered large areas of today's central Mexico and Guatemala,
and may have spread as far south as Peru.
Modern hypotheses have included typhus or typhoid fever, bubonic plague,
measles, and hemorrhagic fever.
One interesting factor is that while the epidemics killed up to 95% of
the local population, some of the Spanish themselves also died.
The Spanish may have had some resistance, but not total.
The DNA in the Cemetery
Two significant papers came out in 2017.
In the first, the researchers reported the discovery of
a specific strain of Salmonella bacteria in the victims.
Salmonella spreads through a fecal-oral route
caused by bad sanitation.
Salmonella enterica genomes recovered from
victims of a major 16th century epidemic in Mexico
They analyzed genetic material from a cemetery containing victims
of the 1545-1550 cocoliztli.
It was at Teposcolula-Yucundaa, in the Mixteca Alta highland area
of Oaxaca in southern Mexico.
The graves had been dug into a thickly built floor at the Grand Plaza,
which is on a mountain ridge above all other settlements and
Historical records report that Teposcolula-Yucundaa was abandoned
around 1552, soon after the end of that epidemic wave.
So, contamination is of very little concern.
In addition, the genetic material is from the pulp chambers of intact teeth,
making it more certain that any bacteria found were circulating in the
victim's blood when they died.
They analyzed material from within the teeth of 29 people.
They also took samples from the surrounding soil for comparison.
Oxygen isotope analysis showed that the victims were local inhabitants.
DNA analysis showed that the victims were infected with
Salmonella enterica Paratyphi C,
a highly human-specific pathogen.
It is not known to inhabit the soil, and none was found
in the soil samples from there or other sites included in the study.
There are over 2,600 varieties of Salmonella enterica,
but only four are restricted to human hosts, where they cause
enteric fever — Salmonella Typhi,
and Salmonella Paratyphi A, B, and C.
Salmonella Typhi and Salmonella Paratyphi A cause
most cases reported today.
Salmonella Paratyphi C, the variety found at the cocoliztli
cemetery, is quite rare today.
A small percentage of people infected, perhaps 1-6%,
become asymptomatic carriers.
They appear healthy while carrying the disease.
This is quite rare for human infectious diseases.
Their theory is that asymptomatic European carriers may have brought
Salmonella Paratyphi C to Mesoamerica in the early to mid 1500s.
Historical documents report that the European conquerors were also
susceptible to the epidemic, although they did not die in
overwhelming proportions like the local people.
An estimated 60-90% of the local Mixtec population died in this epidemic.
That wasn't the only study suggesting Salmonella Paratyphi C
The Pigs in the Past
A different group studying Salmonella Paratyphi C found that
while it's now a human disease largely limited to Africa and Asia,
it also occurred in Europe in past centuries.
They believe that it has been a disease of humans for at least 1,000 years,
likely originating in a transfer from domesticated pigs
in the Neolithic period, the New Stone Age.
Millennia of genomic stability within the invasive
Para C Lineage of Salmonella enterica
They analyzed genetic material from the teeth and long bones of
33 people buried in Trondheim, Norway, between 1100 and 1670 CE.
They found Salmonella enterica DNA in a tooth in one victim.
It was a woman estimated to have died between 1150 and 1250 CE,
when she was 19 to 24 years old.
They also analyzed the δ18Ocarbon isotopes
in her teeth.
That showed that she came from northwest Russia or far northern
inland Scandinavia, arriving in Trondheim by her early teens.
The bacterial DNA from the tooth pulp of the Trondheim woman
was analyzed further.
It was found to be Paratyphi C.
Salmonella enterica Paratyphi C was first recognized in 1916,
when it was isolated from ill eastern European soldiers.
They had enteric fever, also called paratyphoid fever, a severe
and sometimes fatal disease that was common at that time across
northern Africa and the Americas.
It soon disappeared from Europe, except for cases among travelers
returning from East Asia or Africa.
Paratyphi C is a disease unique to humans, but it is part of a broader
Para C Lineage that infects both humans and pigs.
The swine versions have been mostly eradicated from Europe by culling
infected domestic pigs, they only occur in Europe in wild pigs.
We expect bacteria to evolve rapidly.
So it was a surprise when they found that the Salmonella DNA in
the Trondheim woman was almost identical to that in today's
Paratyphi C and related strains.
As their paper title puts it, the Para C Lineage is remarkably stable
So, two conclusions:
First, enteric fever or paratyphoid fever as we know it
today certainly was around in the mid 1500s when the Spanish brought
epidemics vaguely described as "pestilence" to Mesoamerica.
Second, unlike today, the causative Salmonella enterica Paratyphi C
bacteria was present in Europe.
So, one or more asymptomatic Spanish conquistadors could have
carried it across the Atlantic.
Neolithic toilets at Skara Brae in Orkney
They estimated that Paratyphi C may have split from its closest relatives
around 1,100 BCE.
And, that the swine-specific varieties arose during the time that
wild swine were being domesticated in Neolithic Europe.
So, it could have arisen in swine, mutated slightly,
and moved to human hosts.
Beware the Russian Dung Gun