New research suggests that the ancient Mayan civilization fell due to a century-long drought.

The research focused on the analysis of minerals taken from the Great Blue Hole, a famous underwater cave off the coast of Belize, as well as minerals from nearby lagoons. The researchers found that the minerals were indicative of extreme drought that occurred between 800 A.D. and 900 A.D. This time period coincides with the initial collapse of the Mayan civilization.

Those who survived the drought moved to the north, but disappeared a few centuries later. The minerals reveal that this second disappearance also coincides with a major drought, according to Live Science.

André Droxler, an Earth Scientist at Rice University and co-author of the study, and his team drilled cores from the sediments in the Blue Hole of Lighthouse Lagoon and the Rhomboid Reef. The lagoon is surrounded by thick walls of coral reef, keeping surrounding water out in periods of drought. During storms or periods of excessive precipitation, the nearby streams and rivers would flow over the top of the walls, depositing the unique sediments from their riverbeds in the lagoon. Over time these layers pile up and create a chronological record of the climate.

“It’s like a big bucket. It’s a sediment trap,” Droxler told Live Science.

From there, the team analyzed the chemical composition of the sediment cores. In particular, they paid attention to the ratio of titanium to aluminum. During periods of intense rain, titanium from volcanic rocks is swept into nearby bodies of water. Thus, when there is a low ratio of titanium to aluminum, it indicates a period of less rainfall.

Additionally, the team found that during the period between 800 A.D. and 1000 A.D., there were only two tropical cyclones every two decades. That is around a third of the number of cyclones typical to the region and coincide with the beginning of the end of Mayan civilization.

“When you have major droughts, you start to get famine and unrest,” Droxler said.

There have been previous suggestions that the droughts in the region led to the destabilization of the Mayan civilization, however this is the first study to gather data from multiple sites. This study has strengthened the argument that a century-long dry spell brought about the collapse.