A Canadian-led team of scientists has uncovered piles of manure deposited in the Alps by a massive gathering of mammals 2,200 years ago — and they think it solves a longstanding historical mystery.

Carthaginian commander Hannibal famously marched a huge army of soldiers, horses, mules and elephants from Spain, through the Alps to Italy to attack the Romans at the start of the Second Punic War in 218 BC. Historians have argued about his exact route.

But now, a team led by Bill Mahaney, a geologist and professor emeritus at York University, has found what appears to be evidence that Hannibal's army physically left behind.

It seems they passed through the Col de la Traversette on the French/Italian border, as proposed by the British biologist Sir Gavin de Beer decades ago.

"If confirmed, the findings presented here have far-reaching implications for solving the Hannibalic route question and, more importantly, for the identification of a site that might be expected to yield significant historical archaeological data and artifacts related to the Punic invasion," the researchers wrote in the first part of a two-part study published in the journal Archaeometry.

Historical descriptions

Mahaney has been interested in classical history for decades "just as a hobby," he said. He had read about the debate over Hannibal's route, and realized he might be able to figure it out based on descriptions of the environment provided by historical texts. For example, the ancient Greek historian Polybius describes a two-tier rockfall.

Team members (left to right) Bill Mahaney, Chris Allen, Coren Pulleyblank, Jonathan Young and Pierre Tricart took sediment cores from an area called a mire, where rocky terrain gives way to an area of vegetation. (Courtesy Bill Mahaney)

Mahaney scouted Alpine passes and looked for those clues while studying glacial sediments for an unrelated study. Eventually, he found a rockfall and other features that matched the descriptions.

Below the Col de la Traversette was an area called a mire where the rocky terrain gave away to some vegetation and a stream that would have made a good foraging and watering area for animals.

There, Mahaney and his team drilled about 70 centimetres into the soil and pulled up cores of sediment, showing layers deposited over about 3,000 years — including a very unusual layer that looked like it had been completely churned up.

"I said to the other guys, 'You ever seen anything like this?' They just looked at me."

Mahaney said he'd pulled "two or three hundred cores from around the world and I've never seen anything like this.'"

"So this is either frost or one hell of a group of people coming through with animals churning the hell out of this peat."

There was no evidence of frost at nearby sites dating back to that period.

Meanwhile, the unusual layer contained lots of organic material including "some poop – quite a lot of it," Mahaney said.

Horse gut bacteria

Chris Allen, a microbiologist at Queen's University Belfast in Ireland, analyzed the bacteria in the churned up layer and found more than 12 per cent were Clostridia. That type of bacteria typically makes up only two or three per cent of soil bacteria, but represents 70 per cent of the bacteria found in the gut of a horse. The layer also contained unusual levels of bile acids and fats that are typically found in mammal feces. Overall, the evidence suggested deposits of large amounts of horse and mule dung.

Here are some of the routes that historians have proposed Hannibal may have taken through the Alps. New evidence suggests Hannibal passed through the Col de la Traversette on the French/Italian border, as proposed by the British biologist Sir Gavin de Beer. (Bill Mahaney/USGS/NASA/JPL)

"We found scientifically significant evidence of these same bugs in a genetic microbial signature precisely dating to the time of the Punic invasion," said Allen in a news release.

The team did not manage to find any specific evidence of elephant dung.

"You'd have to get very lucky to find that," said Mahaney, noting that Hannibal had only 37 elephants (compared to more than 8,000 horses and mules.)

Carbon dating placed the churned up layer between 26 and 570 BC — the period when Hannibal would have been expected to pass through.

When asked if it was possible that the evidence had been left by some other large group passing through the pass during that time period, Mahaney said there was no reason for any other large army to go through such a high elevation pass. Presumably, he said, smaller groups of humans and animals had used the pass at other times. But they hadn't left a comparable mark in other layers of soil.

Mahaney is now hoping his team will get the funding to go back and take more samples to confirm the dates.

The team is also awaiting analysis of tapeworm eggs found in the ancient dung that could help them pinpoint the geographical origin of the horses that deposited it, since Hannibal's horses were known to come from Spain.

The study was funded by the QUESTOR Centre, Invest Northern Ireland, the Geological Survey of Ireland, the Irish Research Council, Quaternary Surveys, as well as through travel and research grants from York University.