Researchers in Mexico have identified new evidence suggesting that the ancient city of Cuicuilco was deliberately designed in alignment with equinox sunrises, offering fresh insight into early urban planning in Mesoamerica. The findings indicate that the settlement’s layout corresponded closely with solar movements observed during key moments of the year.
The study was led by archaeoastronomer Aaron Uriel Gonzalez Benitez, affiliated with the Astronomical Society of Iztapalapa and Mexico’s National School of Anthropology and History (ENAH). According to the research, structures within Cuicuilco were positioned to align with the rising sun over Cerro Papayo, a prominent hill located to the east, during specific equinoctial periods.
González Benítez identified that these alignments match two significant intervals in the pre-Hispanic Cempohuallapohualli calendar. Known as tozoztontli and teotleco, these periods correspond roughly to dates near March 24 and September 20, rather than the widely recognized equinox dates of March 20 or 21.
Cultural interpretation of equinox alignments
The study highlights that ancient societies did not necessarily follow the modern astronomical definition of the equinox. Instead, they used culturally defined markers based on the sun’s visible movement along the horizon. Gonzalez Benitez distinguishes between the “middle” equinox — calculated as the midpoint between solstices — and the “cultural” equinox, which reflects local traditions and observational practices.
At Cuicuilco B, two key structures, identified as Buildings VI and VIII, appear to support this theory. Their orientation and square design point directly toward Cerro Papayo, aligning with sunrise on March 23 and 24. Previous research had already recognized the hill as an important reference point for solar observation at nearby Cuicuilco A, strengthening the argument that the site was carefully planned around astronomical events.
Experts note that in pre-Hispanic societies, cities were often viewed as symbolic centers of the universe. Architectural layouts, natural landmarks, and celestial patterns were integrated to mark important calendar events and reinforce cultural identity.
Links between ancient and modern alignments
The research also points to a surprising continuity between ancient and modern spatial design in the region. Several buildings on the ENAH campus — including its main structure, annex, library, and research tower — are oriented almost exactly eastward, between 89 and 90 degrees azimuth. Nearby streets in the Isidro Fabela neighborhood follow a similar alignment.
This connection was confirmed during observations conducted on March 23, 2026. González Benítez described the overlap as a remarkable coincidence, suggesting that modern infrastructure may unintentionally echo ancient planning principles.
Jose Manuel Castillo Hernandez, who leads ENAH’s Department of Cultural Dissemination, emphasized the educational importance of the findings.
He said the discovery strengthens ties between the academic institution and the adjacent archaeological site while helping preserve knowledge of pre-Hispanic astronomical traditions. Researchers believe such insights can bring historical science into contemporary classrooms in meaningful ways.