After Alexander the Great perished in 323 BCE, Ptolemy I – a Macedonian Greek general serving under the infamous monarch – rose to become the ruler of Egypt. His dynasty lasted until the legendary suicide-by-asp of Cleopatra VII – yes, that one – along with the successful Roman conquest of the region in 30 BCE.
Francis Ludlow, a climate historian working at Trinity College Dublin, has long suspected that there was more to the fall of the Ptolemaic Kingdom than a successful invasion by the civil war-weary Roman regime. As a new Nature Communications paper by himself and his colleagues has concluded, a volcanic eruption at the time may have been a deciding factor in the fall of the pharaohs.
As they explain, at the time, the kingdom’s prosperity was directly connected with the flow of the river Nile. This is a river that’s fueled primarily by the monsoon rainfall in the highlands of what is now Ethiopia, and each summer, the flooding of said river allowed the arid region to grow its agriculture to its fullest extent.
Writings at the time of the kingdom’s collapse have revealed that the Nile wasn’t flooding like it used to. In fact, according to the Nilometer – the oldest annual hydrological gauge in human history – it was almost running dry, and crops were failing. This caused widespread societal unrest, which catalyzed the fall of the empire. But what stopped the flooding in the first place?
Climate data clearly shows that rainfall is affected by volcanic ash, because it alters air currents, cloud formation, and precipitation locations in potentially troublesome ways. Indeed, as the study notes, “after five twentieth century eruptions, precipitation was suppressed across the Sahel into Ethiopia and in the equatorial regions of Africa that feed the White and Blue Niles.”
The team were curious as to whether this same mechanism applied at the time the ancient superpower met its end. Using ice cores from Greenland and Antarctica, they have previously found sulfur compounds that indicate that several major eruptions were occurring somewhere in the world at the time – although the volcanoes themselves have yet to be identified.