Ancient inhabitants of the Basin of Mexico used it as a precise solar observatory in parliamentary procedure to keep running of the clip of year , a young discipline has concluded . Using the landscape as a calendar , the ancient people were able-bodied to engraft crops at the correct metre of year , and feed a large human population of between 1 and 3 million people .

Before the Spanish infest in 1519 , the study authors write , the Mexica of the Basin of Mexico were able-bodied to bung themselves using advanced agriculture organization . agriculture in the Basin was n’t easygoing , and bank on being able to prognosticate the season . institute too ahead of time , for instance during early rains before the monsoon season , and it will be disastrous for the crops . embed too late and the grow season will be shortened , and your crop will combat sens that have already established themselves during the rain .

As was document by compound encroacher , theAztecswere able to keep track of the twelvemonth fantastically precisely , and may even have know to summate in a spring Clarence Shepard Day Jr. every four years to keep the calendar aligned with the astronomic seasons . What is n’t know is exactly how , but agree to the squad from the University of California , Riverside , it is likely that they used the mountains of the Basin as a " solar observatory " , using the position of the Sun to keep racetrack of the seasons .

“ We conclude they must have stand at a undivided spot , looking eastward from one day to another , to tell the time of yr by determine the rising sun , ” professor of ecology Exequiel Ezcurra , who led the research , said in astatement .

“ Our hypothesis is that they used the whole Valley of Mexico . Their work cat’s-paw was the Basin itself . When the sun rise up at a landmark point behind the Sierras , they knew it was meter to start planting . "

Ancient leaf-book , including the Codex Tovar , Codex Borbonicus , and the Wheel of Boban , make references link Mount Tlaloc and the first day of the new calendar yr , while Spanish writers report that the new class was celebrate when the Sun look over a certain mountain .

Using astronomical models and function of the area , the team was able to simulate the position of the Sun during every 24-hour interval , right back to 4712 BCE . They were able to work out out that on February 24 , the first day of the Aztec young year , a temple at the flock ’s summit and a long causeway structure at its base aligns with the rising sunlight .

" On February 24 , 2022 , we ascended Mount Tlaloc , camp out close to the efflorescence , and climbed to the summit meeting to research the ancient ceremonial bodily structure , " the squad pen in their paper .

" The following day , we ascend the pinnacle once again in the early morning , while still dark , to test the conjunction of the rising sun with the stone - walled causeway . "

The team believes that the precise alignment during the Aztec raw year suggest the ancient mass were using the basin , as well as man - made structures , to keep a precise track of the calendar .

" These results confirm that , even without the celestial cat’s-paw used by Europeans at the time of their arriver ( e.g. , gnomon , scope , quarter-circle , and astrolabe ) , " the team conclude , " the people in the Basin of Mexico could uphold an extremely precise calendar that would have allowed for leap - year allowance merely by using taxonomic observations of break of the day against the eastern hatful of the Basin of Mexico . "

" These results underscore how a similar goal , such as adjust the distance of the calendar to the solar year , " they added , " could be achieved with widely different engineering " .

The study is published inProceedings of the National Academy of Sciences .