An archaeoastronomical study has confirmed that both ancient and contemporary structures at the Cuicuilco Archaeological Zone in southern Mexico City are aligned with equinoctial sunrises, reinforcing theories about the site’s long-standing astronomical significance.
Researchers from Mexico’s National Institute of Anthropology and History (INAH), working through the National School of Anthropology and History (ENAH), suggest that Cuicuilco—one of Mesoamerica’s earliest urban settlements—was deliberately designed in relation to the spring equinox. Central to this alignment is Papayo Hill, where the sun rises during equinoctial dawns.
According to lead researcher Aarón Uriel González Benítez, an archaeoastronomer, the apparent path of the sun over the horizon corresponds with key periods in the pre-Hispanic Cempohuallapohualli calendar. Specifically, the equinox appears to coincide with the Tozoztontli and Teotleco twenty-day cycles, associated with dates close to 24 March and 20 September.
“While the globalisation of the spring equinox links this phenomenon to March 20 or 21, there are other types of equinoxes, such as the ‘middle’ equinox, which indicates the midpoint between the horizontal solstices; or the ‘cultural’ equinox, defined by the contextual calendar of a human group with respect to the equidistance of the apparent path of the sun over the horizon,” he explained.
The study also highlights that several modern ENAH buildings—including its main structure, annex, library, and research tower—share a near-perfect eastward orientation, ranging between 89° and 90° azimuth. This positioning aligns closely with the direction of sunrise during equinoxes. The phenomenon was directly observed and confirmed by the research team on 23 March 2026.
Notably, this alignment extends beyond the ENAH campus. Nearby urban features, such as the grid layout of the Isidro Fabela neighbourhood, also follow a similar orientation. Researchers suggest this may echo much older patterns established by pre-Hispanic structures at Cuicuilco A and B.
Architectural evidence supports this continuity. Buildings within Cuicuilco B display geometric planning and orientations that align with Papayo Hill and equinoctial sunrise points. These features are believed to represent some of the earliest forms of astronomical architecture in the region.
In pre-Hispanic societies, urban centres were often conceived as cosmic hubs, where spatial design reflected celestial cycles. This “architecture–landscape–sun” relationship allowed communities to mark significant calendrical events.
While it remains unclear whether modern urban planning in the area intentionally preserved these alignments, researchers describe the overlap as a striking coincidence. They argue it strengthens Cuicuilco’s identity as a site where ancient knowledge continues to resonate.
Academics at ENAH emphasise that these findings not only preserve cultural memory but also offer valuable educational opportunities, linking contemporary scholarship with Mexico’s pre-Hispanic heritage.
Sources : INAH
