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A History of Mexico City: The Sinking Megalopolis

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J Scull writes biographies and historical articles. Occasionally, he writes about common social issues impacting people in various communit

Mexico City Today

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Tenochtitlan — The Aztec Capital

Mexitli, the war god of the Aztecs, gave his name to part of the land we know as Mexico. A land stretching from just south of the United States to today’s country of Guatemala in the south. The land was ruled by Moctezuma before falling to Spanish conquistador Hernán Cortés in 1521; the year he was killed while imprisoned in his own palace.

Tenochtitlan, the Aztec capital; today’s Mexico City, reflected Moctezuma’s wealth and power. At the time of the Spanish arrival, it was one of the world’s largest cities with a population of 200,000 inhabitants. As a comparison, Beijing, China had approximately 700,000 residents.

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The city traces its history to the 14th century, when Tenochtitlán first became the island capital of the Aztec Empire. It was an astonishing feat of engineering as it was situated on Lake Texcoco in the upland Valley of Mexico. The Aztecs accomplished this by dumping soil into the lagoon and building on the artificial island.

However, the city suffered from flash flooding, heavy seasonal rainfall and saltwater intrusion into the interconnected lakes; events which at times proved devastating to agriculture. Consequently, Aztecs became adroit water-management experts. They built dams and aqueducts that provided fresh potable water; irrigation ditches for agriculture; and canals, causeways and bridges for transportation.

Canals flowed through the city and between raised crop beds creating floating gardens which provided much of the population with food. The Aztecs cleared forests and strategically drained lakes as a way to gain land. However, in doing this, they inadvertently altered the water cycle, resulting in both erosion and increased flooding.

a-history-of-mexico-city-the-sinking-megalopolis

The Conquest and Rebuilding of the City

On February of 1519, Hernán Cortés and his crew landed in modern-day Veracruz. He learned of the great city to the west whose inhabitants were hated by all the tribes the Aztecs considered their vassals. The Spaniards heard of the ruthlessness by which they were treated by the Aztecs. How they were forced to pay extravagant tributes and often used as sacrificial victims; specially the young virgins.

Due to these grievances it became easy for Cortés to persuade the local people to help him destroy Tenochtitlan. However, while these indigenous people saw the Europeans as a way to free themselves from Aztec domination, the conquistadors saw them as future slaves. Ultimately, the indigenous peoples would be more subservient to the Spaniards than they ever were to the Aztecs.

Moctezuma, who had been receiving reports of the new arrivals since their ships first reached the shores of Yucatan, thought Cortés might have been the god Quetzalcoatl. The direction of the ships arrival along with the Spaniard’s light skin, beards and short hair fit a prophecy about the return of this god. This prompted Moctezuma to send gifts to the Spaniards when they arrived in Veracruz.

Cortés and his men arrived in Tenochtitlan on November 8, 1519. They were stunned by its beauty and magnitude. As crowds gathered to look at the strange men and their horses, Moctezuma came out from the center of Tenochtitlan to greet them. The two leaders exchanged gifts. In the hours that followed, Moctezuma continued to shower the visitors with gifts and quartered them in lavish apartments. Perhaps, the deference he showed the Spaniards signaled Cortés that the Aztecs could be easily subjugated.

The comradery both men initially shared did not last long. The Spaniards were horrified by the human sacrifices that were part of the Aztec religious rites. Out of fear Moctezuma would attempt to destroy him and his men, Cortés placed the Aztec leader under house arrest. While Moctezuma was kept captive he was killed. It was initially reported he sustained a severe head injury when one of his own warriors hit him with a rock thrown from a sling. However, this account has been challenged by some historians who claim he was likely strangled by his captors.

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Moctezuma

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Once news spread that Moctezuma had died, the Aztecs rose up against the visitors. The Spaniards tried to flee the city however, many were killed while others were captured and sacrificed by the Aztecs. In spite of the setback, Cortés was determined to lay siege to Tenochtitlan. In Tlaxcala he rebuilt his military forces with the aid of his indigenous allies and in May of 1521 invaded Tenochtitlan. The battle for the city took the better part of three months. Finally in August of 1521, Cuauhtemoc the new Aztec leader, surrendered.

With Tenochtitlan in ruins, the victorious Cortés faced the task of rebuilding Tenochtitlan or building a new city else where. Only Cortés wanted to rebuild the Aztec site as most of the other conquistadors wanted the new city to be closer to the mountains; perhaps an advice he should have heeded. However, Cortés felt that the Aztec islet in the lake was of greater strategic importance. Consequently, the Spaniards began draining the lake and building on top of it. Gradually, the megalopolis that is today Mexico City grew, until the lake completely disappeared.

Flooding, and Environmental Changes

As the Spaniards stripped the hillsides of their trees, mud and silt slid into Lake Texcoco making it shallower than it already was. This not only exacerbated periodic flooding but it began the creation of a soft spongy subsoil. Additionally, the Spaniards had not maintained the Aztec drainage system, which included a dike.

This led to major floods in Mexico City during the years of 1555, 1580, 1604, and 1607. In spite of an 8-mile long drainage system built in 1607 flooding occurrences continued into the mid 1700s. However, at the beginning of the eighteenth century the waters of the lake began to recede. This allowed the city to grow as more land became available for building.

The Sinking City

a-history-of-mexico-city-the-sinking-megalopolis

The Sinking of Mexico City

In the early 1900s scientists began to notice Mexico City was sinking at a rate of 8 centimeters a year. By 1958, that figured jumped to 29 centimeters. In the last two decades, a consistent rate of up to 40 centimeters per year in the city’s historic downtown, has been measured. This has been the result of a geological phenomenon called subsidence, which occurs when too much water is drawn from underground. This causes the land to drop and compact.

Researchers estimate that parts of the city could drop by 20 meters (65 feet) within the next century. Areas adjacent to Mexico City proper could sink 30 meters (100 feet.)

a-history-of-mexico-city-the-sinking-megalopolis

Water

More than 70% of Mexico City’s water supply comes from aquifers below the city. As the city has grown, these underground reservoirs have been draining at a startling rate, leaving empty spaces behind. Because of this, the land has been sinking or subsiding filling these voids. The effects of this phenomenon can be seen all thoughout the city where highways and roads are cracking by the power of the shifting land. Important monuments, historical buildings, cathedrals, even apartment buildings are tilting and cracking. But it is not just at street level where the damage can be seen. Drainage pipes and sewage lines break under the pressure. Subway lines are placed at risk.

Today, the upper layer of clay has already compacted by 17 percent. Experts feel it could ultimately compress by 30 percent within the next 150 years. However, it is estimated the city has gone beyond the point of no return with little that can be done to stop the subsidence. Raising water levels offers no hope for recovering the lost elevation and storage capacity of the aquifers. The continued weight of the city and the further tapping of groundwater will guarantee for the inevitability of further sinking.

Not all parts of the city are sinking equally. While some areas have sunk below the original lake bed, others have remained slightly higher. And this puts the city at higher risk for surfaces to fracture, damaging infrastructure and contaminating water supplies. Exacerbating the problem the city faces is the rain and spring water running off the mountains that surround Mexico City which cause widespread flooding. Experts worry this strong downward flow of water will eventually filter through to the groundwater, introducing pollutants or sewerage.

The long term financial cost of this geological calamity is incalculable. The financial impact of an earthquake is much easier to calculate as it is one solitary event. The sinking of Mexico City, on the other hand, is happening every minute of the day. The city continues to go down relentlessly.

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