In 218 BC, the Carthaginian general Hannibal Barca achieved one of military history's most extraordinary feats - leading an army of 46,000 men, 7,000 horses, and 37 war elephants across the Alps to invade Italy. For over two millennia, the exact route Hannibal took has been fiercely debated among historians and archaeologists. Now, a new study has approached the puzzle from a completely different angle, using movement ecology and bioenergetics to calculate the energy demands of moving such a massive army through the treacherous mountain passes. The findings provide compelling evidence that points to one specific route as the most viable option for the legendary commander.
The team of researchers from the University of Oxford, the German Centre for Integrative Biodiversity Research (iDiv), and the Friedrich Schiller University Jena have published their findings in the prestigious journal Proceedings of the National Academy of Sciences (PNAS). By focusing on the biological realities of the crossing, specifically the immense energy required to move three-ton African elephants up steep inclines, the scientists were able to rank the four most historically debated routes. Their analysis strongly supports the Col de la Traversette as the path Hannibal most likely chose. The study also reveals fascinating details about the physical toll the journey took on both man and beast.
View of the Col de la Traversette, according to the study, the most likely route Hannibal took across the Alps. (Lancebranlette / CC BY-SA 3.0)
Calculating the Cost of War
To determine the most likely route, the researchers modeled the energy expenditure for each of the four main candidates: Col de la Traversette, Col du Clapier, Col de Montgenèvre, and Col du Mont Cenis. They utilized contemporary data on African elephants to estimate the basal metabolic demands and the extra energy required to navigate mountainous terrain.
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The results were pretty clear: the Col de la Traversette, an imposing pass at an altitude of 9,669 feet (2,947 meters) on the modern border between France and Italy, was the most energetically efficient option. The total energy cost for the entire army on this route was calculated at 5.42 terajoules. In comparison, the Col de Montgenèvre would have required 11% more energy, the historically favored Col du Clapier 16% more, and the Col du Mont Cenis a staggering 19% more. Given the severe logistical constraints of feeding tens of thousands of men and animals in hostile territory, minimizing energy expenditure would have been paramount for Hannibal's success.
The Surprising Resilience of Elephants
One of the most intriguing aspects of the study is its revelation about how the different components of the army handled the grueling 15-day crossing. While it has long been assumed that the elephants would have struggled the most, the bioenergetic models suggest otherwise.
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The human soldiers suffered terribly. The researchers calculated that the men would have lost 19% of their body fat reserves during the crossing via the Traversette route, a severe depletion that likely contributed to the high mortality rate; only about half of Hannibal's men survived to reach Italy. The horses also fared poorly, losing an estimated 11% of their fat reserves.
The Col de la Traversette pass today, showing the rugged terrain Hannibal's army would have faced. (Luca Bergamasco / CC BY 3.0)
Surprisingly, the war elephants were biologically better equipped for the journey. According to the models, the elephants would have lost only 4% of their massive fat reserves. As study co-author Dr. Emilio Berti explained, this high energy reserve is likely why many, if not most, of the 37 elephants survived the crossing and were able to fight in the subsequent Battle of the Trebia. Their "four-wheel-drive" biomechanics made them surprisingly adept mountaineers, though keeping them fed through the ensuing Italian winter ultimately proved impossible, and all but one perished.
A New Interdisciplinary Approach to History
The debate over Hannibal's route has raged since antiquity, with the primary sources—Polybius and Livy—writing decades or centuries after the event and providing ambiguous geographical clues. By applying modern movement ecology to ancient history, this study offers a fresh perspective that transcends traditional philological arguments.
While Dr. Berti notes that the analysis "does not eliminate all ambiguity," it significantly strengthens the case for the Col de la Traversette. It demonstrates that this route would have best accommodated the extreme logistical demands of moving a massive, diverse army through the Alps. The study not only brings us closer to solving a 2,200-year-old mystery but also highlights the incredible physical endurance required to execute one of the most audacious military maneuvers in human history.
Top image: Hannibal crossing the Alps on an elephant, painted by Nicolas Poussin. Source: Nicolas Poussin / Public domain
By Gary Manners
References
Berti, E. & Vollrath, F. 2026. Energy costs of Hannibal's alpine crossing. Proceedings of the National Academy of Sciences. Available at: https://www.pnas.org/doi/10.1073/pnas.2612764123
Daily Mail. 2026. Mystery of Hannibal's Alpine march solved? Scientists calculate how 46,000 men and 37 elephants could have made military history's greatest journey. Available at: https://www.dailymail.co.uk/sciencetech/article-14836455/Mystery-Hannibals-Alpine-march-solved-Scientists-calculate-46-000-men-37-elephants-military-historys-greatest-journey.html
Hahn, V. 2026. How did Hannibal get his elephants across the Alps?. University of Jena. Available at: https://www.uni-jena.de/en/how-did-hannibal-get-his-elephants-across-the-alps
PopSci. 2026. Mystery of Hannibal's infamous Alps crossing gets a major clue. Available at: https://www.popsci.com/science/hannibal-cross-alps-elephants-energy/
