Painting of the death of Julius Caesar
Roman dictator Julius Caesar was assassinated during the Ides of March in 44 BCE—about the same time that Mount Etna, Sicily, erupted. Credit: Vincenzo Camuccini/Public Domain

In 44 BCE, a momentous event occurred. Somewhere on Earth, a volcano produced one of the largest eruptions of the past 2,500 years, 2 to 3 times the size of the Tambora eruption that caused the “Year Without a Summer” in 1816. Traces of the eruption can be found in ice cores from Greenland and Antarctica, in the growth rings of trees around the world, and in records of agricultural disaster from Rome and Egypt to China. The eruption caused global climate effects lasting several years.

Also, in Rome, a conspiracy of senators murdered Julius Caesar, and the republic tumbled into civil war.

A group of young researchers says these events may be more closely intertwined than previously thought. Classicists have traditionally focused on the internecine political machinations of the time period and interpreted contemporary descriptions of weird happenings in the sky as metaphor or superstition.

On this episode of the podcast, Rafael Castro, an undergraduate at the University of California, Berkeley, and his colleagues explain why some of the weather and atmospheric effects recorded in ancient Roman poetry seem to describe symptoms of a large volcanic eruption, an environmental disaster that likely exacerbated the impacts of war and contributed to widespread starvation. They think the mysterious eruption is consistent with an event at Mount Etna, a famous volcano in the Roman province of Sicilia (now Sicily), in February of 44 BCE.

Dark Portents

Etna looms 3,336 meters (10,912 feet) over eastern Sicily, about 500 kilometers (300 miles) from Rome. It is the tallest volcano in Europe and one of the most active in the world, with near-continuous rumblings documented over the past 3 millennia.

Ash from the volcano darkened the skies over Rome in the days after Caesar’s bloody end on 15 March, lending gloomy portent to his death and the subsequent turmoil recorded by contemporary writers, according to Morgan King, a professor of classics at the College of St. Benedict and St. John’s University in Minnesota.

Virgil wrote in his four-book farming poem Georgics,

When Caesar died, the great sun pitied Rome
So veiling his bright head, the godless time
Trembled in fear of everlasting night;
And then were portents given of earth and ocean
Vile dogs upon the roads, and hideous
Strange birds, and Aetna quaking, and her fires
Bursting to overflow the Cyclops’ fields

King studies poetry of the Augustan period, named for Caesar’s heir Octavian, who eventually wrangled control and named himself Augustus, first emperor of Rome. She said the people of the ancient world were close readers of nature, watching for aberrations that might signal approval or reproach from the gods.

Ancient writers interpreted the dark skies following Caesar’s murder and, later, the colored halo seen in the heavens when Octavian returned to Rome from what is now Albania as divine commentary on current events. But their observations provide researchers with clues to the physical, as well as the political, environment of the time, King said.

Simulating 44 BCE

Researchers had long noted the correlation of Etna’s 44 BCE eruption and its subsequent environmental effects, but many geologists did not see Etna’s eruption as globally significant because it did not produce dramatic amounts of rock and ash. The massive eruption recorded by the polar ice must be from a volcano somewhere else, researchers thought, and the timing of the Etna eruption mere coincidence.

But Castro and his Berkeley colleagues suggest the key connection may be microscopic particles of sulfate—invisible volcanic emissions with a powerful effect on climate when they rise to the upper atmosphere. Etna is an unusually sulfurous volcano.

Where did volcanic emissions go after the eruption of Mount Etna 2,000 years ago? This animation simulates what may have happened in the winter of 44 BCE on the basis of modern atmospheric models, matching the spread of volcanic emissions to the timeline of reported effects from contemporary records. The blue shows fine particulates, like sulfate, that reach the stratosphere, causing a global cold snap and reflecting the light plants need to grow. The red shows emissions that remain closer to the ground, darkening the skies and causing serious problems for heart and lung health. Credit: Rafael Castro and Noah Randolph-Flagg

To test whether particles pouring forth from Etna could arrive in the right places, at the right times, to match both historical and climate records, Castro simulated their spread with modern atmospheric models. He worked with King to gather historical information from the wider ancient world, looking beyond Rome to Egypt and Southeast Asia for written testimonies, records of crop yields and failures, and even archeological evidence of coin hoarding, which can indicate times were tough.

In the latest episode of AGU’s podcast Third Pod from the Sun, King explains the political and social atmosphere in the Roman Republic at the time of Caesar’s assassination. Castro and geologists Isabel Fendley, Tushar Mittal, and Noah Randolph-Flagg describe why they think Mount Etna is the likely source of widespread environmental disaster in the years following his death.

—Liza Lester (@lizalester), Senior Media Relations Specialist, AGU


Lester, L. (2020), Podcast: Et tu, Etna?, Eos, 101, Published on 24 March 2020.

Text © 2020. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.