CHICHEN ITZA—Archeologists used to wonder why the Mayans vanished around 900 AD. They now believe the cause of the decline to be a sudden tax hike enacted just as the civilization struggled to recover from a drought.

An ancient memo found near the ruins of Uxmal in modern day Mexico tells of infighting among the royal families that ruled the loosely connected city-states of the Yucatan Peninsula.

The Mayans had run up a large debt of cacao beans borrowing from the Teotihuacanese to build their stepped pyramids. At the same time, they were cutting taxes and requesting copious amounts of rain from the gods in order to stimulate their agrarian economy out of a prolonged dry spell.

There was also disagreement on how to balance the annual budget, particularly since they had not yet discovered leap years and so were always a couple days off.

According to Professor Bertram P. Jones, a Mayanologist at Yale University, “Part of the problem was that they used a base 20 numbering system, which made filling out their tax returns a nightmare.”

On top of that, some divine rulers felt that they should make the Mayans at the top of the pyramid share some of their limestone with the community. Others preferred to cut spending on social programs by holding more human sacrifices.

Even though the Mayan central bank developed the concept of zero specifically so it could set interest rates that low, it wasn’t enough to overcome the inaction of the royal households.

The memo found at Uxmal describes a series of automatic tax hikes and spending cuts taking effect. The government both raised the marginal maize tax and also sacrificed 8% more virgins, causing a peasant revolt that brought down the entire civilization.

Says Professor Jones, “The ironic thing is that the Mayans totally predicted this would happen.”