Lunar month intervals at Monte Alban, 496 to 221 BCE, and later Mesoamerican lunar day counts

Many Mesoamerican hieroglyphic texts bear dates in indigenous calendars. Hundreds include dates in a lunation: the most ancient, in Zapotec texts, were observational; the most numerous, in Mayan texts, in a formal lunar calendar. Many Mayan lunar dates were projections into the past or future. Previous research has suggested evidence for specific computing ratios of days to months for such projections; that of 11,960 days to 405 lunations has long been accepted as the quintessential Mayan model for such calculations. This paper addresses observational evidence available to Mesoamerican calendar specialists for developing such models. It uses Lowry’s corpus of lunar first appearances at Monte Alban (650 to 0 BCE) to determine which sequences would have stood out as most reliable observationally, shows that a ratio of 1447 days to 49 months would have been by far the most reliable, and provides circumstantial evidence for its use in Mayan calendrics.