Did a Volcanic Eruption in Alaska Help End the Roman Republic?

Julius Caesar was assassinated in the Ides of March (March 15) in 44 BC. AD and a bloody civil war ensued. This brought down the Roman republic and replaced it with a monarchy headed by the nephew of Caesar Octavian, who in 27 BC became Emperor Augustus. A group of scientists and historians suggest that a massive volcanic eruption in Alaska played a role in this transition, while helping to end Cleopatra’s Egypt.

The study, led by Joseph R McConnell of the Desert Research Institute in Nevada, demonstrates how careful scientific research into the ancient climate can add context to our more traditional research. At the same time, the research raises tough questions about how we fit this data into historical narratives without oversimplifying the story.

Caesar’s assassination came at a time of turmoil for the ancient Mediterranean. This was exacerbated by strange atmospheric phenomena and unusually cold and humid weather that caused crop failures, food shortages, disease and even the failure of the annual Nile flood on which Egyptian agriculture depended. In 1988, the classic Phyllis Forsyth suggested that an eruption of Etna in Sicily in 44 BC.

While McConnell’s team agreed that the Etna eruption could have caused some of these disturbances, they have now argued that it was a subsequent massive eruption from the Okmok volcano in Alaska that altered the climate and contributed to weaken the Roman and Egyptian states. They relied on three pieces of evidence to support their claim.

The first came from samples of ice taken from deep in the Arctic ice caps, which trapped air as they formed over hundreds of thousands of years, providing a datable record of atmospheric conditions. These ice cores showed that there was a peak in solid particles, dust and ash from a volcanic eruption in early 43 BC. The researchers then showed the geochemical properties of these particles in correspondence with samples from the Okmok volcano.

To prove the ancient climate, they then looked at tree rings and speleothems (stalactites and stalagmites) from various parts of the northern hemisphere, including China, Europe, and North America. These suggest that 43BC to 34BC was the fourth coldest decade in the past 2,500 years, and 43BC and 42BC were the second and eighth coldest years.

The research data was then fed into a computerized climate modeling system called the Community Earth System Model (CESM), which produced a climate simulation. This showed that the Okmok eruption could have caused a cooling of 0.7˚C to 7.4˚C in the southern Mediterranean and North Africa in 43-42 BC, which persisted in the 30s BC.

It could also have resulted in increased summer and fall precipitation that damaged crops. At the same time, drier conditions in the upper Nile may have led to its flood failure in 43BC and 42BC.

In this way, McConnell’s team makes the case for Okmok’s potential impact on temperature, precipitation, and a resulting change in crop production in 43 BC and after. But the conclusions they draw from its impact on the whole of history are less certain.

The 10 km-wide caldera on Unmak Island in Alaska formed during the Okmok II eruption of 43 BC.
Kerry Key (Columbia University, New York, NY)

One of the major problems with scientific papers in which climate events are blamed for major historical changes is that they are unable to fit into much of the analysis of historical issues themselves. These tend to be reduced to simple events or problems which can then be easily “explained” or “solved” by science. Realities, when we zoom in, are much messier.

Rome’s transition from a republic to a monarchy – via a period of rule by the competing triumvirate of Octavian, Mark Antony and Lepidus – was a long and complex process. It involved many people and parties with different motivations and plans. The entire period poses a challenge to historians, and entire books have sought to describe and explain it.

But this civil war was only the latest in a series of growing conflicts in the later period of the republic, in which the behavior of earlier figures, like Sylla, who had taken control of Rome decades earlier, became a precedent for what might be possible.

The outcome of the war and the establishment of a monarchy were not inevitable. Rather than a tale of crisis, decline and fall, the period can even be seen as a period of political experimentation, of state formation, of attempts to resolve the issues besetting the republic.

More complicated picture

This wartime period depended on manpower and the ability of the state apparatus to extract and redirect society’s food and money. Despite old sources which report difficulties with this extraction, it should be remembered that the machinery which allowed it has remained mostly in working order. Without it, armies would not have been fed and civil wars could not have taken place.

And while the failure of the Nile floods in 43 BC. Antony and Cleopatra were able to raise and maintain armies, fight and were not finally defeated until 31 BC in the naval battle of Actium. If people were hungry, the conflict itself and the profiteering grain traders were perhaps more to blame than the climate (as was the case during the Ethiopian famines of the 1980s).

The effects of the Okmok eruption in 43 BC may have been severe, as McConnell’s team argues. But it is also very clear that personal, political and military decisions – and chance – have been the direct determinants of the unfolding of history in Rome and Egypt. There were many moments in the years after 44 BC. BC where things could have turned out very differently, whatever the climate.

Military activity in the period alone would appear to show that Rome and Egypt have been quite resilient overall to natural hazards, and as states they have continued to transform in an ever-changing world. .

David C. Barham