As we descended 7m below Mexico City’s Metropolitan Cathedral, I could feel my heart race. I had heard whisperings about the temples buried under this iconic cathedral – one of the largest and oldest in Latin America ­– but since their discovery in the 1970s, it had not been possible to see them. Now, I was part of a public tour that lets visitors explore the ancient secrets that lie just below this church’s depths.

Nearly 500 years after Spanish conquistador Hernán Cortés toppled the Aztec capital of Tenochtitlán, the remains of the ancient metropolis continue to lay hidden mere metres under modern-day Mexico City. The Spanish started building the Metropolitan Cathedral in 1573 above the sacred Aztec (or as they called themselves, “Mexica”) temples as a symbol of their conquest.

When electrical workers accidentally discovered a giant monolith close to the cathedral in 1978, it spurred a five-year excavation that unearthed the Mexica’s spectacular Templo Mayor (“Great Temple”). The discovery and old Spanish records of the Mexica capital’s layout enabled archaeologists to determine that there may be many more pre-Hispanic buildings buried nearby. It also inspired a series of ongoing excavations that continue to unearth new clues about the Mexica’s way of life. Today, many of Mexico City’s more than 21 million residents go about their lives while walking just above the remains of the Mexica city waiting to be uncovered below.

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I held my breath as we made our way down the spiral staircase, exhaling only once my eyes saw the Temple of Tonatiuh, the god of the sun. Tonatiuh was the godly governor in what the Mexica referred to as “the era of the fifth sun” – a period still unfolding that is predicted to end in destruction by earthquake. Given the city’s recent history with quakes, this was a destabilising thought to digest while underground. Nearby, sits the fully intact Piedra Chalchihuitl stone, with a stylised glyph that translates as “the place of the precious or sacred”.

Since 1991, the Urban Archaeology Program (PAU), led by archaeologist Raúl Barrera Rodríguez, has been working nonstop to excavate an area of 500 sq m (about seven blocks of Mexico’s city centre) in order to rediscover Tenochtitlán. Today, whenever workers repair water pipes or install electric cables underground in Mexico City’s centre, by law, the National Institute of Anthropology and History has to be informed so that archaeologists can supervise the proceedings.

“The law gives precedence to archaeology,” said Dr Eduardo Matos Moctezuma, the archaeologist who directed the excavation at El Templo Mayor, starting in 1978. While this makes things complicated for work crews, it ensures that any ancient artefacts are protected.

We can see cracks [in buildings], and we know if we follow those cracks, we might find a pyramid

Findings in the city centre continue to be revealed. A renovation of a building behind the cathedral in 2015 led archaeologists from PAU to uncover el gran tzompantli: a 35m-long skull rack that once had wooden posts where the Mexica displayed the skulls of their sacrificial victims. Over two years of excavations that concluded in 2017, nearly 700 skulls were uncovered, as well as a base with postholes where wooden skull-filled stakes would have been displayed.

In 2017, archaeologists called to a renovation of a hotel in the city’s historic centre discovered an ancient ball court, where the Mexica sent heavy rubber balls flying from end to end using just their hips  during the Juego de Pelota (“Ball Game”). And earlier this year, a number of sacrificial offerings – including the skeleton of a boy dressed as Huitzilopochtli, the Mexica war god – were discovered by the steps of the Templo Mayor. Jaguar bones and layers of shells and coral were also recovered, leading archaeologists to believe that they might be close to finding the tomb of Ahuitzotl, the Mexica emperor who reigned from 1486 to 1502.

Barrera is hopeful that agreements will be reached with the owners of the buildings that stand above both the ball court and the tzompantli so that these vestiges may be on display to the public “in subterranean museums” soon. Since 2018, every Monday, Tuesday and Friday at 14:00, visitors like myself have been able to descend below the cathedral to see the remains of the temples. This tour, run by the cathedral’s guides, helps generate funds for the church while offering visitors an insight into the secret world below one of Mexico City’s most well-known landmarks. (Tickets can be bought from the information desk on the right-hand side as you enter the cathedral.)

We still have the Mexica present in our daily lives

Elsewhere, Mesoamerican vestiges can be found in some unusual places in Mexico City. When changing subway lines in the Metro Pino Suárez station, for example, you’ll pass a pyramid dedicated to Ehécatl, the Mexica god of the wind. On your way out of an underground car park at a shopping centre in the area of Tlatelolco, the site of another Mesoamerican city some 4km from the historic centre, you’ll spot another pyramid also venerating Ehécatl through a viewing window.

Thanks to the records left by the Spanish conquistadors, as well as detailed chronicles written by several Franciscan friars and Mexica diarists, archaeologists have a good sense of where buried Mexica temples and artefacts may be located. Some of the most important information has come from the writings of friar Bernardino de Sahagún in the 16th Century, who described some 78 temples in central Tenochtitlán. “What Sahagún wrote is astonishing because, at an archaeological level, we have been able to find all of what he described,” said Barrera.

Nevertheless, even if you know what might be underneath you, excavating in a city like Mexico’s capital is not easy. The Mexica built their grand urban centre on a small island in the middle of a lake. In some parts of the city, “at 5m deep we have water,” explained Barrera. This waterlogged soil means much of the city centre is sinking some 5-7cm per year – and in some areas as much as 40cm per year. And since certain modern structures are built atop ancient Mesoamerican platforms and structures, it means that not all the city is sinking at the same rate. Just wander around the historic centre and you can see rows of buildings tilting at different angles.

“A number of years ago there was a problem,” Matos explained. “The cathedral started to sink… and the walls started to break because there were pre-Hispanic edifices underneath.” This kind of occurrence, although destructive for colonial buildings and fraught with challenges, can also be helpful to archaeologists, as it helps them identify where Mesoamerican remains might be found.

 

“We can see cracks [in buildings],” said Barrera “and we know if we follow those cracks, we might find a pyramid.” Archaeologists have been able to follow these small fractures “to excavate… and locate the buildings that [were] provoking the [cracking],” explained Matos.

Rather than just chasing cracks, however, new technologies are helping archaeologists make more discoveries. “When we started in 1978, we used theodolites [an instrument used for mapping vertical and horizontal angles],” Matos said. “Now, 3D scanners are used.” Barrera explained that ground-penetration radar is also used to help archaeologists detect what lies beneath the surface of Mexico City’s central streets and plazas. However, Barrera also described how traditional excavation is still often needed to “corroborate what the information and the geophysical scanners show.” The layers of history under the city mean that scanners might appear to find something pre-Hispanic when, in fact, they have landed on a relic from colonial times. Therefore, the only way to be sure is to roll up your sleeves and dig.

It might seem to some that excavating a busy city that’s sinking and is prone to earthquakes is more trouble than it is worth. However, such naysayers “are negating their own history,” said Matos. After all, these excavations have helped reveal that modern-day Mexico City bares many similarities to ancient Tenochtitlán.

Many of the historic buildings at the core of today’s sprawling metropolis serve the same function as they did almost 700 years ago. There’s the Spanish cathedral built atop the Mexica temple; while Mexico’s National Palace, where the current president lives, stands above the ruins of the palace of Moctezuma II, the long-standing Mexica emperor who was killed in the early stages of the Spanish conquest. “It is very important because it remains the seat of power, from Moctezuma II to today,” said Barrera. “It is very symbolic.”

Barrera also described how a university was built where a Mesoamerican school once stood, and the Mexica city would have had a central plaza that played much the same role as the modern Zócalo. “We still have the Mexica present in our daily lives,” he explained.  

It’s quite incredible to imagine that a city founded in 1325 would have so much in common with the chaotic megalopolis of today, but one thing is for sure: a Mesoamerican heartbeat still pulses just under the surface of modern-day Mexico City.

Unearthed is a BBC Travel series that searches the world for newly discovered archaeological wonders that few people have ever seen.

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