LAUSR

Significance Without the navigational and calendric instruments of the 16th century Europeans (like gnomon, compass, quadrant, or astrolabe), the inhabitants of the Basin of Mexico were able to keep an accurate agricultural calendar that allowed them to plan their agricultural cycle to feed one of the largest population densities on Earth, as well as maintaining rituals associated to the solar seasons. To achieve this, they used the rugged topography of the Basin as a precise solar observatory and also built a high-altitude stone causeway for accurate adjustments of their calendar to the solar year. These results underscore how a similar goal, such as adjusting the length of the calendar to the solar year, could be achieved with widely different technologies.