Project Lyobaa - Results from the first 2022 Season
On May 12 2023, the Project Lyobaa research team presented the results of the first phase of the geophysical scan of the archaeological site of Mitla, Oaxaca, aimed at uncovering evidence of a system of caves and passageways underneath the site, considered by the ancient Zapotecs to be an entrance to the Underworld, or Lyobaa.
Project Lyobaa is the result of an institutional collaboration between the Mexican National Institute of History and Anthropology (INAH), the National Autonomous University of Mexico (UNAM) and the Association for Archaeological Research and Exploration, ARX Project, A.C.
The project employed three different geophysical methods for scanning the site, including Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT) and Seismic Noise Tomography.
For the first time in Mexico, results snd images generated from these three methods were combined to provide an accurate 3D model of what lies beneath the ground.
The results were summarized in a research report delivered to the INAH Council of Archaeology in January 2023 and first officially revealed in a press conference held on May 12, 2023.
The findings confirm the existence of extensive underground chambers and tunnels underneath the Church Group of the ancient site, in the same location claimed by Colonial documents and the local tradition to be the entrance to the great subterranean temple of Lyobaa.
Additionally, the study has revealed evidence of an earlier construction stage of the Palace of the Columns, Mitla’s most important and best preserved ancient monument, as well as several other geophysical anomalies that may be interpreted as tombs or buried archaeological structures.
These findings will help rewrite the history of the origins of Mitla and its development as an ancient site, as well as providing valuable information for the management and prevention of seismic and geological risk in the area.
An entrance to the Underworld under the Church?
In 1674, the Dominican father Francisco de Burgoa described the exploration of the ruins of Mitla and their subterranean chambers by a group of Spanish missionaries. Burgoa’s account speaks of a vast subterranean temple consisting of four interconnected chambers, containing the tombs of the high priests and the kings of Teozapotlán. From the last subterranean chamber, a stone door led into a deep cavern extending thirty leagues below ground. This cavern was intersected by other passages like streets, its roof supported by pillars. According to Burgoa, the missionaries had all entrances to this underground labyrinth sealed, leaving only the palaces standing above ground.
In order to verify the local tradition that the main altar of the Catholic church conceals the entrance to the underground labyrinth, the patios and groups of structures around the church were investigated with geophysical methods. Various arrays of electrodes and geophones were installed around the church to create a 3D image of what may lie below the ground.
Both methods confirmed the existence of a large void located right beneath the main altar and extending in northwesterly and westerly direction. This void appears to be connected with another significant geophysical anomaly located immediately to the north of the church.
The electrical tomography further revealed the existence of two east-west oriented passages entering the main void from the east, at a depth of between 5 and 8 meters.
The arrangement of chambers and tunnels underneath the church displays a far greater and more complex articulation than the relatively simple cruciform chambers that exist under the Columns Group and in other parts of the site. Both the depth and orientation of the newly identified chambers (northeast-southwest instead of north-south), suggest that they may not have been originally connected to the buildings above ground, all of which share a predominantly north-south or east-west orientation.
A possible blocked up entrance was identified underneath the main altar of the Catholic church.
Findings in the Columns Group
The geophysical scan of the Columns Group did not reveal any significant subterranean anomalies. A few meters to the north of the Palace stairway, however, both Ground Penetrating Radar and Electrical tomography revealed the profile of what appears to be an earlier stairway leading to a portico with two doorways. The evidence is compatible with an earlier construction stage of the Palace of the Columns, which was hitherto believed to have been constructed entirely in the Postclassic period (ca. 900-1200 CE), but that may have had its origins in the late Classic period.
Some fairly regular GPR anomalies in the area of the Patio of the Columns and the Patio of Tombs suggest the possible existence of earlier archaeological structures and a different position of the central altar. A linear anomaly immediately to the south of the north platform of the Patio of Tombs appears to be directly associated with one of the two monumental tombs located in this patio. The anomaly appears aligned with the tomb but in a southerly direction, whereas the tomb itself extends underneath the north platform. This anomaly, which is also evident in the ERT scan of the same area, appears to be associated with a deep trench possibly dug by archaeologists or treasure hunters in the past century.
New research already under way
For the month of September 2023, the same joint research team formed of the ARX Project, INAH and UNAM is planning a second season of geophysical investigation at Mitla, focused on the remaining groups of structures to the west and south. These include some of the earliest monumental architecture at Mitla, in the Calvario (or Adobe) and South Group. The Arroyo Group will also be scanned in search of possible subterranean chambers.
The team is hopeful that permission may be granted by the local community and Church authorities to conduct further geophysical scans in the area of the church of San Pablo with greater image resolution.
We would like to thank for the successful conclusion of the first season of Project Lyobaa at Mitla all the personnel from the Mexican National Institute of History and Anthropology (INAH), Centro INAH Oaxaca, Zona Arqueológica de Mitla, Corredor Arqueológico Valle de Tlacolula (COVATLAO) and Department of Geophysical Engineering of the Faculty of Engineering of the National Autonomous University of Mexico (UNAM).
Special thanks and our heartfelt gratitude also to the local community and guides of San Pablo Villa de Mitla for their generous hospitality and support throughout this project.
Funding for this project was provided by the Association for Archaeological Research and Exploration, ARX Project A.C., with the contribution of over 60 independent donors that participated in our crowdfunding campaign.