Photo taken on March 26 shows a volcano covered by snow at the Ulan Hada volcano group in north China's Inner Mongolia Autonomous Region. Photo: Xinhua/Peng Yuan

The assassination of Julius Caesar in 44BC triggered a nearly two-decade power struggle that led to the fall of the Roman Republic and the rise of the Roman Empire.

Historic records say the period was marked with strange sightings in the sky, unusually cold weather and widespread famine - and a new study suggests a volcanic eruption in Alaska may have been the cause.

The paper was published in the Proceedings of the National Academy of Sciences on Monday.

An international team of scientists and historians used an analysis of volcanic ash (tephra) found in Arctic ice cores to link the period of unexplained extreme climate in the Mediterranean with the crater-forming eruption of Alaska's Okmok volcano in 43BC.

"To find evidence that a volcano on the other side of the Earth erupted and effectively contributed to the demise of the Romans and the Egyptians and the rise of the Roman Empire is fascinating," said lead author Joe McConnell of the Desert Research Institute in Reno, Nevada.

The advent of the Roman Empire also brought an end to the dynasty of Ptolemies, the last of the pharaohs.

"It certainly shows how interconnected the world was even 2,000 years ago," added McConnell.

He and Swiss researcher Michael Sigl began investigating the matter when they found an unusually well-preserved layer of ash in an ice core sample in 2019.

New measurements were then made on ice cores from Greenland and Russia, some of which were drilled in the 1990s and stored in archives.

They were able to make out two distinct eruptions: a powerful but localized and short-lived event in early 45BC, followed by a much larger, more widespread event in 43BC, with fallout lasting more than two years.

A geochemical analysis was performed on the ash samples found in ice from the second eruption, and it perfectly matched the Okmok event - one of the largest eruptions of the past 2,500 years.

"The tephra match doesn't get any better," said volcanologist Gill Plunkett from Queen's University Belfast. The team gathered more supporting evidence from across the world, from tree-ring- based climate records in Scandinavia to cave formations in Northeast China.