Decades of drought in the sixth century AD brought chaos, political unrest, war and eventually the fall of the ancient southern Arabian kingdom of Himyar. It was the perfect breeding ground for Islam.

The once mighty kingdom of Himyar collapsed about 1,500 years ago after a period of turmoil and crisis. It was conquered by the neighboring kingdom of Aksum (now Ethiopia). A previously overlooked reason, namely a long period of extreme drought, seems to have contributed to this upheaval and the rise and spread of Islam in the centuries that followed.

petrified water
The research team at the University of Basel led by Professor Dominik Fleitmann analyzed the layers of a stalagmite from Al Hoota Cave in present-day Oman. The growth rate of the stalagmite and the chemical composition of the limestone layers allowed them to determine how much precipitation has fallen over the cave in the past. These limestone deposits thus contain a wealth of information about the climate from centuries ago.

“Even with the naked eye you can tell from the stalagmite that there must have been a very dry period of decades,” says Fleitmann. When less water drips through the strata onto the stalagmite, the pillar grows with a smaller diameter than in years with a higher drip rate.

In addition to the size, the isotopic composition of the different layers in the stalagmite is also relevant. The more it rains in tropical and subtropical regions, the more of the lighter oxygen isotope 16O is found in the limestone. In a drier period, relatively more 18O is deposited in the stalagmite.

In order to determine how much and when it rained, a uranium-thorium dating was performed on the stalagmite as a third measuring method. For example, the team found that not only was there less rainfall over a longer period of time, but that there was even extreme drought in the early sixth century AD, with an accuracy of 30 years.

Stalagmites are dripstone cones that have grown up from the ground. Source: svrid79

murder case
“A direct correlation between this drought and the collapse of the Himyar kingdom cannot be established from this data alone,” Fleitmann explains. Therefore, he conducted additional research using historical sources, in collaboration with other historians. In this way he arrived at a more accurate climate reconstruction of the region.

“It was a bit like a murder case: we have a dead kingdom and are looking for the culprit. Step by step, new evidence brought us closer to the answer,” says the researcher. Helpful resources included records of the Dead Sea’s water level and historical documents describing a multi-year drought in the region, dating back to AD 520. This gave the team more and more evidence to support their theory.

“Water is the most important thing there is. A decline in rainfall over decades could destabilize a fragile semi-desert kingdom,” Fleitmann said. In addition, the irrigation systems required constant maintenance and repairs. This is only possible with tens of thousands of well-organized workers. Due to the water shortage, the people of Himyar were probably no longer able to do this, which made the situation even worse.

Historic turning point
When we think of extreme weather events, we are often talking about a short period of at most a few years. That changes in climate can lead to the destabilization of states and changes of power is something we rarely think about. However, extreme weather can change the course of history.

“The population endured many hardships as a result of famine and war. This led to fertile soil for Islam. The population was looking for something hopeful that could bring people back together as a society. The new religion had this in it.” You cannot say that the drought was the direct reason for the rise of Islam, the researcher emphasizes. “But it was an important factor in the context of the revolutions in the Arab world of the sixth century.”