In 218 B.C. the Carthaginian general Hannibal led an army of 30,000 soldiers, 15,000 horses and mules and 37 war elephants across the Alps into Italy, a bold move that led to one of the greatest victories of the Second Punic War with Rome. It placed Hannibal in the pantheon of legendary ancient generals like Alexander the Great and Julius Caesar.
The crossing is still studied by military tacticians today, but the details are a bit hazy. Historians have speculated for centuries about exactly what route the Carthaginian army took through the mountains, but there has been no solid proof. Now, microbial evidence from horse manure may point to Hannibal’s hair-raising route.
A study published in the journal Archaeometry shows that a “mass animal deposition” took place in the Col de Traversette, a 9,800-foot pass on the modern border between France and Italy around 200 B.C. Microbiologists from Queen’s University in Belfast sampled soil from a peaty area near the top of the pass, the type of place that an army might stop to water its horses. What they found was a disturbed layer of peat about 40 cm down that was not churned up by natural occurrences like a flock of sheep or frost, according to a press release.
They also found the soil layer was full bacteria usually associated with horse manure. “Over 70% of the microbes in horse dung are from a group known as Clostridia and we found these microbes in very high numbers in the bed of excrement,” writes study co-author Chris Allen of Queens University in an article for The Conversation. “Much lower levels of Clostridia genes were found elsewhere at the site." The bacteria can survive for thousands of years in the soil, which allowed the researchers to identify the creatures through partial sequencing of their genes.
This wasn’t just a random find, reports Philip Ball at The Guardian. The study’s leader, Bill Mahaney, a geomorphologist at York University in Toronto, has studied Hannibal’s route for almost 2 decades. Based on ancient sources like Polybius and Livy, which recount the army’s harrowing journey along narrow paths and over steep slopes, he was able to develop certain terrain features to look for. In particular, there is a passage in Polybius that discusses a double rockslide that obstructed the pass.
In 2004, Mahaney began looking at satellite photos of the various routes proposed by historians, including a more northerly path near present day Grenoble. But after analyzing the photos and several trips to the various sites, Mahaney concluded that the Col de Traversette was the route that most closely matched the ancient texts. In 2011, Mahaney and his team began exploring the bog area and eventually unearthed the layer of horse manure.
Now the team will look for even more evidence at the site, hoping that coins, belt buckles or even a sword or two will emerge from the peat to confirm their microbial evidence. Already the team has uncovered what may turn out to be a horse tapeworm egg from the manure, Chris Allen tells Ball.
“There is even the possibility of finding an elephant tapeworm egg,” he says. “This would really be the pot of gold at the end of the rainbow.”