Monday, November 29

The feat of removing and replacing the collapsed roof in the Templo Mayor of the Aztecs

“With a historic hailstorm, the roof of the Casa de las Águilas has just collapsed in the Archaeological Zone of the Templo Mayor. I go there with the director of the venue to assess possible damage. All the security and conservation team mobilized, ”wrote archaeologist Leonardo López Luján, director of the Templo Mayor Project, on the rainy night of April 29, 2021. The steel roof that protected the Casa de las Águilas – a 15th-century building richly decorated and of prime importance in the religious life of Tenochtitlan – it had been flattened in book form on the floor. Thank the gods, he did not damage anything fundamental in the archaeological structure. Six months after that day, the maneuvers to remove the cover have begun. It will take about six more to completely replace it with a new one.

Workers on top of a scaffold waiting to climb the collapsed roof structure of the Casa de las Águilas.
Workers on top of a scaffold waiting to climb the collapsed roof structure of the Casa de las Águilas.Aurea Del Rosario

The process of removing a specialized roof in a World Heritage area – the entire Historic Center of Mexico City has been, since 1987 – on a building over 500 years old, on a lake floor, in a seismic zone , with recurring rains, in the midst of a pandemic and with a stucco made with nopal slime, stones and a little sand without damaging it hardly is a real feat. “Since the incident occurred, we have not stopped being aware of space, which is very fragile in itself. The first thing we did was assess the damage and make decisions to protect, on the one hand, a larger settlement from the collapsed roof itself and, on the other, from the rains that were already beginning; at the same time, it was necessary to evaluate how the roof was going to be raised and what kind of new roof was required for the House ”, Patricia Ledesma, director of the Museo del Templo Mayor, explains to EL PAÍS.

Crane used to remove the structure covered the House of Eagles in the Templo Mayor.  INAH has begun reconstruction to avoid damage to murals and fences.
Crane used to remove the structure covered the House of Eagles in the Templo Mayor. INAH has begun reconstruction to avoid damage to murals and fences.Aurea Del Rosario

The collapse occurred two days before the WHO warned of the “worrying” state of the pandemic in Latin America. The experts had to count the damage with their healthy distance in an already small space. Then, process permits with the local government so that large and heavy material such as scaffolding, a specialized crane or steel bars, could be handled and transported in an area protected by UNESCO. The task involved, for example, the urban planner Iris Infante, head of works at the National Institute of Anthropology and History (INAH); the head of restoration, Maricarmen Castro and the famous archaeologists Eduardo Matos Moctezuma and Leonardo López Luján. The director of INAH, Diego Prieto, and the National Coordinator of Historical Monuments, Valeria Valero Pié. Archaeologists, restorers, engineers, architects and geotechnicians joined to make decisions about the maneuvers to remove and define the new roof without forgetting the artistic and historical regulations of the enclosure.

While the guidelines were being reviewed and the operation was planned, the site had to be protected. “What interests us is not the roof, but what is underneath, especially the stucco that is very fragile and porous, so you have to constantly monitor the humidity, the Mexicans themselves had trouble keeping the coating in good condition” , summarizes the director of the Templo Mayor. “We were also concerned about the polychromy inside, in fact, the cover had helped prevent the passage of ultraviolet rays and protect the colors of the ornaments,” explains to this newspaper Mariana Díaz de León Lastras, head of restoration of the Museum and the archaeological zone of the Templo Mayor. For this reason, the first decision made by the specialists consisted of putting a liner on the entire floor of the Casa de las Águilas, an enclosure that stands out for “its isolation from the outside, its scarce lighting and its reduced dimensions”, as described the archaeologist López Luján, which speaks to us of “an atmosphere of recollection suitable for activities such as prayer, meditation and penance. Furthermore, the rich interior decoration indicates that the blood offering was one of the main ceremonies that took place there ”.

Then, we proceeded to formwork, that is to say, box the walls and sidewalks, which are also important for their beautiful reliefs. Once the wood had been protected and had an anti-fire and antifungal treatment, piles were placed, capable of regulating the level of the roof. The dismantling of the old and the installation of the new cover has been entrusted to TGC Geotecnia, a company specialized in soil mechanics, which has been in charge of the geometric correction of the Sagrario and the Metropolitan Cathedral; the re-foundation of the National Palace, the analysis of the subsoil of the Independence Monument or the displacement of a large house from 1929 cataloged by the National Institute of Fine Arts (INBA) to build the Reforma Tower, to mention some of the most important monument works . In addition to the roof, the perimeter fence, which was damaged that day in April, will be changed and studies will begin to restore the roofs of two other temples. The one that most worries archaeologists is the one that covers the second construction stage of the old pyramid of the Templo Mayor, the Huey Teocalli, the largest after the one that covered the Casa de las Águilas, designed by the architect Pedro Ramírez, had supported the great earthquakes of 1985 and 2017, but the hailstorms and their 40-year life have made the tubes that support the roofs angled and obsolete.

Workers on the collapsed roof that covered the House of Eagles in the Templo Mayor
Workers on the collapsed roof that covered the House of Eagles in the Templo MayorAurea Del Rosario

“The current cover will be removed in 12 sections, which will be cut out like a big cake. What the engineers do is cut the tridilose – a highly lightweight three-dimensional structure system and roof top layer – which is then tied and adjusted to the crane so that there will be no movement from the rest of the roof, and finally , it is manually cut into smaller pieces ”, explains restorer Mariana Díaz de León. This Monday the first section was withdrawn; Although the archaeological zone measures one hectare, everything is full of archaeological floors and buildings classified as World Heritage, so the mobility space is very limited. Luckily, the Casa de las Águilas is next to the vehicular stream, which allows carrying heavy machinery at night and not damaging anything around it.

The replacement will be identical to the roof designed by Ramírez Vázquez. It is contemplated that the cover continues to respect the visuals, that it filters UV rays and takes care of the air vents, all this with the least amount of supports possible. “We are in an archaeological zone, you cannot be making holes like cheese either roquefort, that was also a great challenge that engineers and architects had to face. What is going to change is the material, which is going to be lighter. After 40 years, there are better materials that can help us, but the design is going to be very similar, it is planned that we will finish the work in approximately six months ”, concludes the director Patricia Ledesma.

The compound of the eagle warriors, the building that served the Mexica nobility, the tlatoani and their court, was built in stages, like its neighbor, the imposing Templo Mayor. According to the Aztec worldview, Huitzilopochtli – lord of war and god of the sun – represented many times as an eagle, led men to the promised land from Aztlán. The signal to found the new city was to find an eagle on a cactus devouring a snake. The roof perhaps not only protected the House of the Eagles, but the myth that tells that the Mexica received the signal from Huitzilopochtli to build the great Tenochtitlan.

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