The Mayans lived in present-day Guatemala and Honduras around 800 years ago
The first civilization to use 0 as a place holder
Technically, the Mayans created a 360-day calendar but decided that there were 5 more days, but on those days the gods left them and they were unprotected.
They used terracing and irrigation
There are many different theories of the Mayans disappearing on of the most logical ones are that since the Mayans were such violent, warlike people war makes sense. They could have been killed down to low numbers by a giant tribe.
The Mayans, though technologically advanced, weren't the best doctors to ever so an unknown and untreated disease could knock out an entire civilization quite quickly.