The leap-year concept in the first descriptions of the Aztec calendar (Examination of early Spanish misconceptions of Mesoamerican calendrical descriptions)

The dates of a number of sources prove that the Aztecs did not make interca lations, but we also find a limited number of sources using the same dates. It is exactly in these sources that we find the European calendrical conce pt of making intercalations. It is hypothesized that the leap year concept is partly owing to the first calendrical description which probably was made in a leap year. Other error s of this first calendar were the first Veintena of the year and a misplace ment of twenty days of the Aztec year. A Veintena is an Aztec month of twen ty days. It resulted in a confusing picture of the Aztec calendar. Later so urces tried to remedy these misunderstandings of the Aztec calendar, but th ey also added new ones, where the most significant feature was to assign th e festival to the first day of the Veintena, instead of the last. Andres de Olmos may have been the author of an early source called The Moto linia Insert I, where the leap day falls upon the European leap day and whe re the festivals were celebrated upon the first day of the Veintenas. Alrea dy by 1540 Toribio de Benavente y Motolinia discarded the leap year concept and the concept of celebrating the festivals upon the first day of the Vei ntena, but the misconceived calendar concept of Olmos persisted and was cop ied into a number of sources.