More than 2,200 years after Hannibal launched one of recorded history’s most daring military campaigns, leading roughly 46,000 soldiers and 37 war elephants across the towering Alps between modern-day France and Italy to invade the Roman Republic. Now, researchers believe they may have uncovered a surprising clue to one of antiquity’s greatest military mysteries.
For generations, historians have debated exactly which Alpine pass Hannibal used during his legendary crossing in 218 BC before descending into Italy and launching a campaign that brought Rome to the brink of defeat during the Second Punic War.
Any equally enduring mystery has been why the legendary Carthaginian general would burden his army with 37 war elephants, each weighing roughly three tons (about 6,600 pounds), while attempting one of the most difficult mountain crossings in military history?
A new study published in the Proceedings of the National Academy of Sciences suggests those two mysteries may actually be connected.
Rather than relying entirely on ancient accounts, particularly those of the Greek historian Polybius, or on geology and topography, researchers analyzed the energy required for Hannibal’s soldiers, horses, and elephants to traverse four leading candidate routes through the Alps.
Their findings show that the notoriously difficult Col de la Traversette was actually the most energy-efficient crossing—and that the elephants, far from being a crippling liability, may have been better suited for the journey as opposed to either the soldiers or the horses accompanying them.
The discovery provides a new perspective on one of history’s greatest military feats, suggesting that the biological limits of both humans and animals may help explain not only where Hannibal crossed the Alps, but why he believed his extraordinary gamble could succeed.
“Our analysis of the energy landscape challenging the army suggests that the Col de la Traversette would have been the shortest and energetically most efficient route,” researchers write. “In which case, driven by the aim to minimize the energy costs of the crossing, he would have chosen the Traversette route.”
Hannibal’s campaign remains one of history’s most astonishing logistical achievements. After marching roughly 620 miles (1,000 kilometers) from Spain, his force reached the Alps with approximately 46,000 soldiers and 37 war elephants.
The crossing reportedly took just 15 days despite hostile tribes, steep mountain passes, early winter conditions, and severe supply challenges. Only about half of the army survived the journey, although enough elephants reached Italy to participate in the Battle of the Trebia shortly afterward.
Researchers examined four leading candidate routes through the Alps by estimating the total energy required for each member of Hannibal’s expedition, including the soldiers, horses, and elephants accompanying them.
Rather than asking which mountain pass best matches ancient historical accounts, the researchers examined four leading candidate routes through the Alps, calculating the energy required for every member of Hannibal’s expedition—including his soldiers, horses, and war elephants.
Using models that consider elevation changes and the metabolic costs of climbing and descending, they calculated the total energy expenditure for men, horses, and elephants across each candidate route. The results consistently favored the Col de la Traversette.
The researchers estimate the entire army would have expended approximately 5.42 terajoules of energy along that route. By comparison, taking the Col du Clapier—long considered by many historians to be the strongest candidate—would have required roughly 16% more energy.
Even the second-best alternative would have demanded 11% more. A chart in the paper compares the cumulative energy costs of each route, showing the Traversette path retaining the lowest overall expenditure despite its dramatic elevation profile.
Although Hannibal obviously lacked modern mathematical models, the researchers suggest he likely had an instinctive insight into terrain developed through years of campaigning.
“Although Hannibal would not have had such accurate estimates, he may have had a qualitative understanding of the ranking of the possible routes,” researchers note.
Perhaps the study’s most fascinating insights concern the elephants themselves.
Modern elephants require enormous quantities of food simply to maintain their body weight. Wild African elephants typically spend around 14 hours each day feeding, while a three-ton adult may consume roughly 440 pounds (200 kilos) of forage daily. Those requirements become even more daunting in mountainous terrain, where every climb increases energy demands.
The researchers estimate that each elephant would have expended an additional 1.53 gigajoules of energy simply from traversing the Col de la Traversette beyond its normal metabolic requirements. Replacing that energy through feeding alone would have required roughly five to six extra hours of foraging every day during the crossing.
That simply was not realistic.
Instead, the team concludes that Hannibal’s elephants almost certainly survived by drawing heavily on stored body fat rather than replacing the calories they were burning. Even then, the elephants appear to have been surprisingly well-suited for the journey.
According to the analysis, each elephant would have lost only about 4% of its body fat reserves during the Traversee crossing. Horses, by contrast, were estimated to lose around 11%, while surviving soldiers may have lost approximately 19% of their stored fat. Even on less efficient routes, the additional burden fell disproportionately on the men and horses rather than the elephants.
That finding helps explain an apparent historical paradox.
For generations, historians have wondered why Hannibal would risk bringing massive elephants across one of Europe’s most formidable mountain ranges. This new study argues that, biologically, elephants may actually have handled the journey better than many of the humans accompanying them.
Modern biomechanical research has shown that elephants move like a four-wheel-drive vehicle, enabling them to navigate difficult terrain more effectively than many might expect. Their large fat reserves also provided an energy buffer unavailable to exhausted soldiers.
“We may assume that Hannibal knew, after having traveled with elephants and their handlers through Spain and Southern France, that his elephants would struggle less than his men to make the crossing,” researchers note.
Researchers argue that the greatest challenge facing Carthage’s war elephants came after they crossed the Alps, not during the journey itself.
Once in Italy, Hannibal found himself deep inside enemy territory with no secure supply lines, making it extraordinarily difficult to replenish the elephants’ depleted energy reserves. Historical evidence suggests his army was forced to raid the surrounding countryside extensively to feed both its soldiers and animals.
Although the elephants survived the Alpine crossing, researchers say the enormous logistical burden of keeping them fed may have ultimately sealed their fate.
“The fact that all but one elephant died in the following winter might be indicative of Hannibal’s decision to stop attending to the energy needs of such costly pieces of military equipment when already under severe energetic constraints,” the researchers write.
The researchers suggest the elephants’ greatest value may have reached beyond their battlefield role. Simply bringing dozens of war elephants across the Alps would have delivered a powerful psychological advantage, both by surprising Roman forces and by demonstrating the extraordinary reach of Hannibal’s army.
But that advantage may have been short-lived. Once the initial shock passed, the enormous cost of feeding and upkeep of the animals deep inside enemy territory may have exceeded their military usefulness.
Taken together, the evidence suggests that the same biological realities that influenced Hannibal’s choice of route may also have determined the fate of his most famous weapons.
“Perhaps he counted on the elephants to provide an important, tactical element of surprise in the first battles against the Romans,” the researchers write. “In addition, he may have expected that his war elephants would awe and help recruit to his side the Celts of Northern Italy, who were known to be hostile to Rome.”
“After these first encounters, the elephants might have lost their military value,” the team adds.
The paper, “Energy costs of Hannibal’s alpine crossing,” by Emilio Bertia and Fritz Vollrath, appeared in Proceedings of the National Academy of Sciences.
Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan. Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com