​The Ancient Poop Trail of Conquerors
Renaissance fresco depicting Hannibal’s Alps crossing. Image: Getty Images


This story is over 5 years old.


​The Ancient Poop Trail of Conquerors

Where did Hannibal cross the Alps? Follow the trail of ancient horse poop.

The Carthaginian general Hannibal lived over 2,200 years ago, yet his legacy continues to cast an immense shadow over modern history and culture. Brimming with hatred for Rome, the charismatic commander staged an invasion in 218 BCE that famously involved marching an estimated 30,000 troops, 15,000 horses, and 37 elephants over the Alps.

Caught completely off guard by Hannibal's flamboyantly bold approach, the Romans suffered a series of devastating defeats that almost cost them their burgeoning empire. Emboldened by the success of his crossing, Hannibal rampaged through his enemy's defenses, crippling the Roman army with an excruciatingly well-executed pincer move at the Battle of Cannae in 216 BCE.


Though the great general would ultimately lose the Carthaginian-Roman conflict, called the Second Punic War, to his worthy rival Scipio Africanus, Hannibal's brash yet cunning style is still emulated by modern military strategists, and the nightmare of his invasion haunted the Roman empire for the rest of its existence.

But while many ancient writers documented Hannibal's elephantine march, the exact route he took has been contested for centuries. Now, in an exciting development, an international team led by geomorphologist Bill Mahaney of York University may have finally cracked this longstanding cold case.

In a study published this week in Archaeometry, Mahaney and his colleagues describe a floodplain bog near the Col de la Traversette, a mountain pass perched a dizzying 3,000 meters above sea level on the French/Italian border. The site contains compelling evidence of what the team calls a "mass animal deposition," suggesting that the area was once disrupted by an enormous throng of humans and animals that stopped to camp there, exactly around the time Hannibal made his fateful lunge for Rome.

What's more, the team found abundant evidence of Clostridia bacteria, which is a major component of horse manure. While this is not an unequivocable slam dunk confirming that Hannibal crossed there, it does represent the first tangible evidence of this notorious march recovered from the Alps.


"The microbiological remains […] are clearly well preserved," Chris Allen, a microbiologist at Queen's University Belfast and a co-author of the study, told me. "Most Clostridia produce endospores—basically microscopic, highly stable, genetic pods that can morph into living bacteria if the conditions are right."

"These things can survive remarkable physical conditions," he added. "This is accepted by the scientific community. So I am not surprised at all that they are still there after 2,000-plus years."

Indeed, it's somewhat more challenging to understand why a trail of ancient horse dung is the only firm remnant that has ever been recovered from Hannibal's death-defying maneuver. Surely an army comprised of thousands of men and animals would have littered its trail with corpses and artifacts?

"It is always difficult to explain a negative result," Allen explained. "I think that Hannibal's army was really the crack troops of their day. Even at the scale they were at, I wouldn't imagine they left a lot of hard evidence behind."

But even troops as disciplined as Hannibal's couldn't help but leave a trail of fecal detritus in its wake. The fact that Mahaney's team has been able to pick up this path is exciting enough on its own merits, but it also offers a lens through which to view historical events beyond Hannibal's crossing.

"The organic [chemistry] and microbiological end could be used to work up other sites in the ancient world and even in the New World," Mahaney told me. "Anywhere there is some evidence that people occupied a site even for a few days, as with Hannibal. One could follow sites identified by Julius Caesar in his logs and use the biotic signals to find sites worth geoarchaeological exploration."


"We think our approach is quite novel," Allen said. "It may well be applied to other similar situations, but there are various factors that need to be satisfied. For example, critical in this case was the fact that this is a highly undisturbed site."

Finding similarly unruffled sites, rich in bacterial samples, can help fill out the story of these murky ancient events, and add valuable context to the movements of the world's most influential leaders. Evidently, captivating texts are hidden in the Earth, written in the language of life, which can augment what we know from historical texts and accounts.

In this case, the site has validated Mahaney's longstanding theory that Hannibal made his route through the Col de la Traversette, which he outlined in his 2008 book Hannibal's Odyssey: Environmental Background to the Alpine Invasion of Italia. This path was first championed by British biologist Sir Gavin de Beer some 60 years ago, but has remained controversial in academic circles.

To that point, the study's authors have more work to do before they can conclusively declare that Hannibal's forces once camped at the bog below the Col de la Traversette. For instance, Allen is currently leading a "full scale metagenomic analysis" of the samples extracted from the ancient bog to get a firmer grasp on their origins and identity.

"I think ultimately only a full scale excavation of the site will satisfy all the experts," Allen told me. "That will probably be down to the French. The area is part of a National Park, we were very lucky to get permission to investigate the site to begin with. This was largely down to one of the co-authors—Pierre Tricart from Grenoble."

What these future efforts and expeditions will turn up remains to be seen. But if the site is conclusively proved to have been visited by Hannibal and his army of Punic vengeance, one of the most significant outstanding mysteries in military history will finally be resolved.