Project Belguie Xiguie | Teotitlan del Valle

Ancient Layers Revealed: Pre-Hispanic Settlement Hidden Beneath Teotitlán del Valle

by Kayla Kurin

August 28, 2026

A Geophysical Map is helping archaeologists understand the zapotec history that’s still underground at the Belguie archaeological site

Around 30 km southeast of Oaxaca de Juárez lies Teotitlán del Valle (Xiguie). In the Tlacolula Valley Archaeological Corridor, the small town holds on to traditions influenced by Zapotec, Mixtec, and Aztec history. It’s known for its textile art, traditional dance, and the Belguie archaeological site. The site houses centuries of zapotec heritage, but has, in great part, remained a mystery until now.

Archaeologists have found evidence of a series of chambers that may indicate a burial site, walls that made up the Northern part of the palatial complex, and an ancient canal. The geophysical map made one thing clear: there’s more to the site than we can currently see.

Denisse Argote, one of the lead researchers on the project, told us that this project has helped “Make the invisible visible in a way that is respectful of the environment of Teotitlán del Valle.”

Surrounded by green mountains and rolling valleys, a towering white and red colonial church is at the centre of the site. Over the past years, the structure of the church has been damaged by earthquakes, indicating an unstable foundation. This has led researchers to ask: what more of the original Zapotec site lies under the Church compelx and central square of Teotitlan?

Traditionally, to answer this question, archaeologists would need to excavate. But that would destroy the historical colonial heritage of the area and disrupt the modern streets where 6000 residents live. ARX Project worked with a dedicated team of scientists from INAH and UNAM to use non-invasive technologies to build a 3D archaeological map of the site.

“These technologies are radically transforming the discipline of archaeology by enabling surgical, predictive excavation planning, as well as providing information that could not otherwise be obtained,” Argote said.

Figure 1. GPR scanning the area in front of the church of Our Lady of Nativity, in the center of Teotitlán del Valle (Marco M. Vigato)

A Town Built Upon Another Town

There’s a reason a site as important as Teotitlán del Valle, a ceremonial centre with monumental architecture and stelae dating back to the Classical period, lacks an archaeological map. Teotitlán del Valle is a town built upon another town.

Today, the modern village sits on ancient Mesoamerican foundations. The original archaeological core is hidden beneath streets, plazas, and the church complex of Our Lady of Nativity.

The site contains three historical layers and was most active during the Classic (500-1250) and Postclassic (1250-1521) periods.

The majority of the archaeological artefacts and structures are concentrated in three main locations:

The walls of the Nativity Church, where pre-Hispanic architectural elements decorated with step-fret motifs and carved stelae are embedded.
A plot adjacent to the south side of the church complex where there is a partially excavated and restored pre-Hispanic platform displaying a Zapotec-style talud-tablero structure.
The community museum, which preserves and displays numerous stelae, step-frets, and other stone elements, along with ceramic pieces found over the years by the community.

The excavated portion of this site, known as Belguie, ”Fire Serpent”, in Zapotec, is interpreted as the rear section of the main temple of the pre-Hispanic settlement. These material remains demonstrate the existence of monumental ceremonial and palatial architecture concentrated precisely where the civic and religious centre of the colonial town was established.

Figure 2. The study area in the center of Teotitlán del Valle (Courtesy: A. García Kobeh)

The Central Block is a Stratified Archive of 20,000 Square Meters, including six prospecting zones:
● Zone A: Belguie Archaeological Site (3,150 m²)
● Zone B: Temple and Parish House (3,486 m²)
● Zone C: Church Atrium (2,697 m²)
● Zone D: Civic Plaza (3,640 m²)
● Zone E: Community Museum (2,965 m²)
● Zone F: Municipal Palace (4,151 m²)

Figure 3. The Xiguie archaeological site, in the center of Teotitlán del Valle (Marco M. Vigato)

The Great Zapotec Platform

The most exciting find from the survey is the Great Zapotec Platform. 3D models show large rigid bodies beneath the Church and Atrium, which gives us a clearer picture of what the layout of the original zapotec settlement looked like.

Argote explained that the shape of these underground units is very particular. “They form a kind of rigid “ring”, indicating that the monumental structures once surrounded a large courtyard.” These shapes support the hypothesis that the pre-Hispanic architecture was partially destroyed or modified during the colonial period to build the church complex.

Figure 4. 3D ERT scan of the Nativity church, showing a possible stepped platform buried beneath the Colonial buildings (Courtesy: Andrés Tejero Andrade/ UNAM)

The 3D Electrical Resistivity Tomography scans show us what kind of structures lie beneath the surface. “The elongated rigid body detected in the middle area of the atrium, oriented east-west, points to another similar platform, likely a second courtyard or continuous palace space, echoing the system of adjoining plazas characteristic of regional archaeological sites like Mitla,” Argote said.

This reveals a pattern of continuity and overlap of sacred and power spaces, where the New Spain civic-religious center was deliberately built on top of Zapotec ceremonial architecture.

The Electrical Resistivity Tomography (ERT-3D) study at the Belguie site detected an anomaly whose shape suggests the presence of a tunnel-like structure with two partially filled chambers. In the context of Oaxaca's Central Valleys, this feature is of great importance, as it is highly consistent with a Zapotec-style funerary chamber system. If confirmed, this finding would reveal a spiritual, ancestor-worship dimension at the very heart of the monumental area, providing key information about the funerary practices of the elite who inhabited the settlement.

Figure 5. ERT scan cross-section of the Belguie archaeological site, showing possible buried archaeological features.

Ceremonial Patios and Palatial Structures

Our team also looked under the Priest’s house for the remains of the ancient northern building of the palace, which would close the pre-Hispanic complex on that side. Because of the location of the church and the carved stones found in its walls, we thought that this part of the structure may still be underground.

Thanks to 3D ERT scans, it was possible to see through the layers of earth and discover that the church rests upon what appears to be a stepped pre-Hispanic structure. In the most superficial layer, around 40cm underground, the radar detected mainly colonial-era infrastructure. However, at 90cm depth, an ancient floor level was discovered, hidden beneath a thick layer of rubble and stones, suggesting that architects of the church brought large quantities of fill to level the terrain before building. At a depth of 2.5 metres in the church interior, traces of great importance appear when the data are overlaid with a current map of the temple. The stepped platform is found at approximately 3 meters depth and appears to be the continuation of the palatial complex.

Figure 6. GPR profile of the investigated areas inside and around the Church of the Nativity, showing linear alignments suggestive of ancient wall foundations.

Alignments suggestive of ancient living spaces or rooms were detected. These could be remains of a pre-hispanic temple or, conversely, structures designed to provide stability to the foundations of the church complex.

An Ancient Canal

Researchers were surprised to find something unusual beneath the civic plaza: two perfectly straight parallel lines running east to west. Geophysical cross-sections to confirm the finding showed defined edges, suggesting it is not a natural watercourse but a designed work that would have had a strategic connection.

The canal is located just a few meters from the pre-hispanic platform and points directly toward the river. This is likely a fragment of the water system designed by the ancient Zapotec and could have served to carry water from the ceremonial centre to the river.

“Discovering the technical brilliance of the ancient inhabitants through the geometry of that ancient hydraulic channel more than two meters deep, or finding the stepped structure and the anomaly suggesting a system of funerary chambers at the Belguie site, is archaeologically moving,” Argote said.

This ancient channel, oriented toward the Teotitlán River, reveals something entirely new about the technical capabilities of its inhabitants: the existence of a complex hydraulic system designed to control and divert water.

Figure 7. GPR profile of the ancient canal at a depth of 2.5 meters under the municipal palace.

What's Next?

The key archaeological findings: The previously unknown palace structures, funerary chambers, and an ancient canal demonstrate the continued importance of this site to local communities and the preservation of the past.

In the next phase, the researchers will use the 3D models for field validation and action. Argote explained the team is excited for the possibility of, “Conducting direct, controlled archaeological explorations to confirm the nature of the underground chambers and tunnel.”

Our team will continue research in this area, working with Teotitlán del Valle's Municipal Presidency, the Community Museum Committee, and the Catholic Temple Committee, and build on the team's earlier two research seasons at Mitla, Oaxaca (Project Lyobaa 2022 and 2023 seasons).

Román Gutierrez Ruiz, president of the Teotitlan del Valle community museum, told members of the project team, "We are deeply grateful for this project and for the support it has received. For us Zapotec, this area that they are studying is very important. We are very interested in seeing more of our ancient roots."

What The Ground Tells Us In Teotitlán Del Valle

by Kayla Kurin

August 28, 2026

In Teotitlán del Valle, ancient Zapotec and colonial stones tell us a lot about the history of the place and its people, but as strong as these layers of foundations may look, they are not immune to the forces of nature.

On August 2, 2025, a magnitude 5.9 earthquake hit Teotitlán del Valle. The community found that the ground beneath the Church of Santa Maria la Navidad lacked stability. The Church is at risk for damage from future earthquakes. Understanding the Zapotec builders from around the year 1200 is the key to saving it.

Researchers from INAH and UNAM used non-invasive technologies – GPR, Electrical Tomography, and Ambient Seismic Noise, to see through centuries of complex stratigraphy without moving a single stone. Not only were they able to create an archaeological map of the area, but they were also able to assess weaknesses in the ground to understand why the Church may be at higher risk from earthquakes.

Andrés Tejero-Andrade, a researcher on the project, told us, “ERT-3D has been in use in Mexico for about 10 years, during which time it has achieved very important successes, opening up new opportunities to explore archaeological sites while reducing costs.”

Archaeology Without A Shovel

Three non-invasive technologies allow us to read the subsoil in high resolution:

Denisse Argote, a lead researcher on the project, explained, “These technologies are radically transforming the discipline of archaeology by enabling surgical, predictive excavation planning. This technology will help democratize knowledge, allowing findings to be shared with local communities through visually understandable 3D models that strengthen cultural identity and long-term participatory conservation.”

Preventing Future Damage

The Church of Santa María la Natividad suffered earthquake damage because it was built on an unstable ground transition caused by the juxtaposition of colonial fill against an ancient Zapotec platform. Its frequency creates a local amplification effect that caused the differential movements in the domes during the 2025 earthquake.

● Structure (Triaxial Seismograph): Natural frequency of the church: 7.5–8.5 Hz

● Ground (MASW): Dominant vibration frequency of the fill terrain: 4–8 Hz

The passive vibration study revealed that the church structure and the ground on which it rests vibrate at almost the same fundamental frequency. When an earthquake occurs, the ground and the building amplify each other. This resonance dramatically increases the structural vulnerability of the historic church to future seismic events.

Subsoil Heterogeneity and Velocity Contrast

Figure 7. Seismic tomography scan of the Church and Atrium, showing a critical low-velocity anomaly (dark blue) located in front of and beneath the church’s front façade (Courtesy: Martín Cárdenas Soto)

Figure 8. High resistivity (Red) and low resistivity (Blue) bodies to the west and south of the Church and archaeological site.

Marked heterogeneity detected with abrupt lateral variations over short distances.
Critical Anomaly: A circular low-velocity zone (Vs ~250 m/s) located exactly in front of and beneath the church's front facade.
Contrast: Toward the south and the museum, the ground is much more rigid (Vs = 700–800 m/s).
Interpretation: This suggests the church rests on ancient fill and loose materials, while the surroundings have pre-Hispanic platforms or more compact rock.

Figure 9. 3D model of the high resistivity (Red) and low resistivity (blue) bodies under the center of Teotitlan del Valle. The white lines over the study area indicate the boundaries of the main buildings and courtyards.

The Future Of Non-Invasive Research

Argote told us, “By cross-referencing data from different geophysical methods, specialists will not only recover history but will also be able to simultaneously identify structural vulnerabilities in historic monuments caused by subsoil heterogeneity, designing comprehensive conservation solutions against threats such as seismic risk.”

The hope is that these technologies will help archaeologists uncover more ancient sites without affecting modern architecture. These tools can be used before modern infrastructure work to help avoid building newer structures atop historic centers.

Archaeologically, these tools will continue to help researchers to design fieldwork strategies with a higher success rate without breaking ground. Some of the benefits of using these technologies include:

Absolute protection of heritage: By using methods such as ground-penetrating radar (GPR), electrical resistivity tomography (ERT), and passive seismic surveying (PASW), the integrity of the underlying archaeological remains is guaranteed without risk of damage or destruction.

Feasibility in built-up areas: These methods allowed deep analysis directly beneath historic monuments still in use, such as the walls, domes, and floor of the Church of Our Lady of the Nativity or the flagstone floors of the atrium — places where traditional excavation would be architecturally and socially unfeasible.

Safety and non-damaging coupling: For data collection on sensitive surfaces (such as historic courtyards or areas of the temple's roof), traditional rods and geophones were replaced with flat steel electrodes with water-soluble gel and metal disk plates, achieving optimal ground contact without drilling into or altering a single centimeter of the original structure.

Efficiency and resource optimization: These tools make it possible to survey large areas of land in a short amount of time. By generating three-dimensional maps and models of subsurface anomalies, the spatial distribution and depth of cultural features can be precisely determined, optimizing the selection of future excavation strategies with a much higher probability of success. This saves time, money, and human resources.

Putting Research Into Action

The findings beneath the Catholic Church complex show that the church was built atop of a monumental pre-hispanic platform. “The builders dismantled the pre-existing indigenous structures, reused their materials, and filled in the uneven areas with large volumes of rubble and earth to create a raised, uniform base,” Argote said.

Now that researchers know the reason for the instability of the church, they’re recommending a strategic reinforcement plan. It’s not enough to patch the cracks, the soil must be stabilized to reduce the differential movement.

The museum, at risk for water damage from the back wall that sustains part of the vast colonial fill of the ancient zapotec platform, also needs support. Gutters need to be installed and joints need to be sealed to protect the walls from damage from rainwater.

We hope the subsurface maps will become the basis for a structural engineering plan. This will make it possible to design soil consolidation or improvement protocols needed to stabilize the facade of the Church of the Nativity and save its domes from future disasters, as well as implement the recommended rain gutters to curb the moisture saturation threatening the walls of the Community Museum.

This project is not only about better understanding the past, but preserving the architecture we have in the present so that this important historical site can be enjoyed by local communities and visitors for generations to come. Argote said, “The greatest hope is to share these results with the community of Teotitlan, integrating this subsurface map into local civil protection and urban development plans so that the past continues to safeguard the town's future.”

Acknowledgments

We would like to express our most heartfelt gratitude to the entire project team:

Dr. Denisse Argote Espino (INAH), Arq. Leobardo Pacheco Arias (INAH), Arq. Uriel Sánchez Sosa (INAH), Dr. Andrés Tejero Andrade (UNAM), Dr. Martin Cárdenas Soto (UNAM), Dr. Gerardo Cifuentes Nava (UNAM), Dr. Aidé Esmeralda Lopez (UNAM), M.Sc. David Escobedo Zenil (UNAM), Eng. Alejandro García Serrano (UNAM), Eng. Jesús Sánchez González (UNAM), Dra. Ana Luz Caccavari Garza, graduate students Alejandro García Kobeh, Carlos Quitze Sandoval Miranda, and Felipe Guevara Peralta.

Special thanks also to the personnel of the Corredor Arqueológico Vale de Tlacolula INAH-Covatlao, Centro INAH Oaxaca, Municipality of Teotitlán del Valle and the Municipal President, Mr. Felipe Hernández Vicente , Comité del Museo Comunitario and its President, Mr. Román Gutiérrez Ruíz, Comité del Templo Católico and its President, Mr. Manuel Ruíz Martínez.

Also, a huge appreciation goes to the over 75 donors and sponsors who generously contributed to our fundraising campaign and who helped with their donations to cover for part of the costs of this second season of Project Lyobaa.

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