Fifteen centuries ago, extreme dry conditions contributed to the decline of the ancient South Arabian kingdom of Himyar. Combined with political unrest and war, the droughts left behind a region in disarray, thereby helping to create the conditions on the Arabian peninsula that made possible the spread of the newly emerging religion of Islam. The research, led by the University of Basel in collaboration with the University of Massachusetts Amherst, was recently reported in the journal Science.
Credit Fleitmann et al.
On the plateaus of Yemen, traces of the Himyarite Kingdom can still be found today: terraced fields and dams formed part of a particularly sophisticated irrigation system, transforming the semi-desert into fertile fields. Himyar was an established part of South Arabia for several centuries.
However, despite its former strength, during the sixth century CE, the kingdom entered into a period of crisis, which culminated in its conquest by the neighboring kingdom of Aksum (now Ethiopia). A previously overlooked factor—extreme drought, may have been decisive in contributing to the upheavals in ancient Arabia from which Islam emerged during the seventh century.
Dominick Fleitmann, professor of environmental sciences at the University of Basel and the lead author of the study, analyzed the layers of a stalagmite from the Al Hoota Cave in present-day Oman. The stalagmite’s growth rate and the chemical composition of its layers are directly related to how much precipitation falls above the cave. As a result, the shape and isotopic composition of the deposited layers of a stalagmite represent a valuable record of historical climate.
“Even with the naked eye you can see from the stalagmite that there must have been a very dry period lasting several decades,” says Fleitmann. When less water drips onto the stalagmite, less of it runs down the sides. The stone’s diameter is smaller in droughty years than in wetter years when the drip rate is higher.
Furthermore, isotopic analysis of the stalagmites layers allows researchers to draw conclusions about annual rainfall amounts. For example, they discovered not only that less rain fell over a longer period, but that there must have been an extreme drought. Based on the radioactive decay of uranium, the researchers were able to date this dry period to the early sixth century CE.
The Himyarite Kingdom depended heavily on an extensive and complex irrigation system, which required constant maintenance and repairs, and which could only be achieved with tens of thousands of well-organized workers. The population of Himyar, stricken by water scarcity, was presumably no longer able to ensure this laborious maintenance, aggravating the situation further.
Political unrest in its own territory and a war between its northern neighbors, the Byzantine and Sasanian Empires, spilling over into Himyar, further weakened the kingdom. When its western neighbor of Aksum finally invaded Himyar and conquered the realm, the formerly powerful state definitively lost significance.
Research 25 Years in the Making
Credit: Fleitmann et al.
“Part of what makes this work so exciting,” says Stephen Burns, professor of geosciences at UMass Amherst and one of the paper’s co-authors, “is its multi-disciplinary aspect.” Only within the past twenty years or so, Burns says, have paleoclimatologists, archaeologists and historians begun to work closely together. “As we started talking, we came to realize that climate history is an important factor in the history of human civilization.”
Publication is especially sweet for Burns because Fleitmann was his first graduate student. “We began this research over 25 years ago,” says Burns. When Burns, who began his career at the University of Bern, came to UMass Amherst in 2001, Fleitmann followed soon afterward as a post-doctoral fellow. “We’ve been collaborating for most of my career,” says Burns.
It was during his post-doc at UMass Amherst that Fleitmann also met Raymond Bradley, Distinguished Professor of geosciences at UMass Amherst and one of the paper’s co-authors. “One can’t ignore the reality that the environment and society are deeply intertwined,” he says. “This research has opened a new window into the past, and now, using the analyses that Fleitmann and Burns have helped develop, we can really zoom in to the decade level to see how the environment and society interacted.”
“When we think of extreme weather events, we often think only of a short period afterwards, limited to a few years,” Fleitmann says, but a much longer drought could lead to much greater social and political destabilization, which in turn could create a power vacuum and the opportunity for a new institution that could bring people together again as a society.
All the researchers are quick to point out that environmental factors alone cannot explain the rise of Islam, or of any faith. “However,” says Fleitmann, “drought was an important factor in the context of the upheavals in the Arabian world of the sixth century.”