Nahua Calendars

Before the Spanish conquest, the Nahuas used two interlocking calendar systems: a 365-day solar calendar (xiuhpohualli) and a 260-day ritual calendar (tonalpohualli).¹ Following the conquest, Spanish colonial authorities suppressed indigenous calendar use due to its connections to pre-Christian religious practice.² As a result, the Catholic parish records featured in this tutorial use only the Julian/Gregorian calendars, and researchers will not encounter the indigenous calendar system in these documents.

Aztec Sun Stone or Piedra de Sol is often referred to as a Calendar Stone. While it has calendar elements (like the 20 days signs of the 260 day calendar) it wasn’t used as a timekeeping device, but rather a sacrificial alter dedicated to the sun God Tonatiuh.³

The dates found in most colonial Nahuatl parish records follow the Gregorian calendar which is the same calendar used throughout the world today. Spain adopted the Gregorian calendar on October 15, 1582, by decree of Philip II, making it the standard calendar used in New Spain and its parishes from that point forward. Because the vast majority of colonial Nahuatl parish records date from after 1582, researchers will find that dates in these documents — day names, month names, and year numbers — are immediately readable without any conversion: unlike researchers working with English colonial documents, who must contend with the Julian calendar used in England until 1752.
For researchers who encounter records dated before October 1582, those dates follow the Julian calendar, which runs 10 days behind the Gregorian calendar.⁴ In such cases, a common genealogical practice in writing and citation is to record the date exactly as it appears in the original document and note that it follows the Julian calendar, rather than converting it, to avoid confusion when cross-referencing against the original source.

Image: Gary Lee Todd, Aztec Sun Stone or Calendar Stone, photograph, 4 July 2012, Aztec (Mexica) Gallery, INAH, National Museum of Anthropology, Mexico City, Wikimedia Commons, CC0 1.0 Universal Public Domain Dedication, accessed 15 July 2026. https://commons.wikimedia.org/wiki/File:Aztec_Sun_Stone_or_Calendar_Stone.jpg.