Hannibal’s crossing of the Alps has confounded historians for two millennia. The legendary Carthaginian commander somehow got more than 30,000 troops, 15,000 horses and mules, and 37 elephants up and over the mountains and into enemy territory. Now researchers claim they can confirm where he did it, thanks to the biological evidence the horses left behind. The study appears online in the journal Archaeometry.

Romans and Carthaginians battled in the Second Punic War from 218 to 201 BCE. In the first year of the battle, Hannibal set his sights on Roman Italy. Had the Romans known of his plans, they might have laughed; after all, Hannibal and his troops stood on the other side of an enormous mountain range.

But it would be Hannibal who had the last laugh in this story. He led his party up the treacherous slopes, losing many men and animals along the way. Somewhere amid the impassible peaks, he found a way through. But where? Scholars and men of history, including Napoleon, have offered many theories, but there’s been no evidence—until now.

Using genetic analysis, environmental chemistry, pollen analysis, and geomorphic investigation, scientists have identified what they call a “mass deposition event” near a pass known today as the Col de la Traversette. (By “mass deposition,” they mean that a whole bunch of animals pooped in the same place at the same time.)

"The deposition lies within a churned-up mass from a 1-metre thick alluvial mire, produced by the constant movement of thousands of animals and humans,” co-author Chris Allen said in a press statement. “Over 70 percent of the microbes in horse manure are from a group known as the Clostridia, that are very stable in soil—surviving for thousands of years. We found scientifically significant evidence of these same bugs in a genetic microbial signature precisely dating to the time of the Punic invasion."

In addition to the microbial evidence, the height of the pass—nearly two miles above sea level—makes it fairly unlikely that an enormous group of defecating animals had assembled there by coincidence.

The researchers also found signs of horse tapeworms in the manure. Analysis of the muck is still ongoing, but they’re crossing their fingers for elephant turds. “There is even the possibility of finding an elephant tapeworm egg,” Allen told The Guardian. "This would really be the pot of gold at the end of the rainbow."

Long before he found any evidence, lead author Bill Mahaney had spent an awful lot of time thinking about Hannibal. In addition to this study, Mahaney is also the author of The Warmaker, a novel about Hannibal’s crossing of the Alps.

“I have been in the field for long times with 100 people, and I can tell you it can be pandemonium,” Mahaney told The Guardian. “How Hannibal managed to get thousands of men, horses and mules, and 37 elephants over the Alps is one magnificent feat.”