No Aztec or colonial source states a rationale for the count's length. Proposed links to the human gestation period and to the synodic period of Venus are modern scholarly proposals rather than attested Aztec explanations, and they do not agree with each other.
What would resolve this A Nahuatl source, colonial or pre-conquest, that states a reason for the 260 day length rather than only describing its mechanics would settle which explanation, if either, the Aztecs themselves held.
Resolution The entity's own cycle-length fact answers this directly: 260 days is 20 named day signs paired with the numbers 1 through 13 (20 x 13 = 260), an attested structural fact already carried on Aztec Tonalpohualli. · 08/08/2026 12:00:00 AM
ResolvedMesoamerican archaeology; Nahuatl philologyDavid Carrasco, Religions of Mesoamerica, 2nd edition