Hannibal’s Elephants Took the Cheapest Route Across the Alps

A new study has estimated the energy Hannibal’s army expended hauling itself, along with its war elephants, across the Alps in 218 BC. Of the possible routes, one was markedly less costly than all the others.

Among the Alpine passes available to him, the Col de la Traversette would have required the least energy from his army.

The finding brings biological evidence to a question that historians have disputed for centuries through ancient writings and Alpine geology. It also challenges a widespread belief: the elephants, rather than the soldiers, were the force’s best-equipped members for enduring the mountains.

The cheapest Alpine crossing for Hannibal’s elephants

The research was carried out by Emilio Berti at the German Centre for Integrative Biodiversity Research in Leipzig.

Instead of arguing over which valley best matches the ancient descriptions, the team created an energy landscape: a map showing the energy demanded by every step taken along a route.

Using elevation information collected by NASA satellites, they entered the terrain into a model that calculates the energetic cost of walking uphill and downhill for bodies of specified mass. They then applied it to a 3-tonne elephant, a horse and an infantryman travelling over four potential passes.

The Traversette route performed best by every measure. Its closest competitor would have required roughly 11% more energy from the entire army, while the most punishing pass would have cost about 19% more.

The difference remained consistent whether the calculations considered elephants, horses or men.

Traversette demanded the least energy

For years, scholars generally favoured another route, the Col du Clapier, as Hannibal’s most likely crossing point. More recent interpretations of the ancient texts and the terrain have shifted support towards the Traversette, and the energy calculations now point in the same direction.

The uphill sections are the costly ones, and elephants would normally avoid them.

A previous GPS study of wild African elephants showed that they detour around even mild gradients. The new calculations indicate that, for an animal of such great mass, even a modest rise creates a genuine energy obstacle.

Yet the elephants fared better than either horses or men. On the Traversette, an elephant would have used only around 4% of its fat reserves, compared with approximately 11% for a horse and almost one fifth for a man.

Hannibal’s elephants burned less fat

Their size explains the apparent contradiction. An elephant possesses such extensive fat reserves that 15 days of strenuous walking would scarcely deplete them, whereas a lean soldier had far less available before those losses began to have serious effects.

Restoring those reserves was the real difficulty. In the wild, a 3-tonne elephant consumes about 200 kilograms of vegetation each day merely to cover its basic requirements. Eating that quantity takes many hours of continuous feeding.

The exertion of the ascent would have required another five or six hours of feeding daily. No marching army could have permitted such near-constant foraging. Since that was impossible, the elephants had to draw on the fat reserves they brought with them.

Why did Hannibal bring elephants?

One question has proved more enduring than the rest. People continue to ask not only how Hannibal managed to cross with elephants, but why he attempted it when keeping the animals alive was so expensive.

Historians, geographers and classical scholars have debated the crossing for generations. One recent examination of this prolonged disagreement describes it as a debate that becomes more precise rather than reaching a conclusion.

Hannibal’s previous experience alone gave him grounds to believe the plan could succeed. He had already led the elephants across Spain and southern France, so he knew they could cope with mountainous terrain better than his men.

Their anatomy also offered an advantage. A study of elephant legs found that their limbs remain elastic and flexible even while walking, functioning more like a four-wheel-drive vehicle than rigid pillars. This construction is better suited to slow, heavily laden movement on steep ground than it might first seem.

Hannibal himself rode an Asian elephant called Surus, larger than the African elephants from the Atlas Mountains that formed most of the herd. Its name is among the few individual details of the march that have survived.

He may also have relied on more than the animals’ physical strength. Their appearance could unnerve Roman troops in the first battles. It may likewise have encouraged the Celtic peoples of northern Italy, long hostile to Rome, to join his cause.

Winter killed most of Hannibal’s elephants

Transporting the elephants over the Alps ultimately proved to be the easier task. The army entered the mountains with 37 animals, and about 30 survived to fight at the Battle of the Trebia shortly after the descent. Hannibal won that battle as the Romans panicked at the sight of the elephants.

Every one of those survivors apart from Surus died during the following Italian winter. The crossing, once seen as the greatest danger, was less lethal than the cold and hungry months that followed.

This outcome matches the study’s severe calculations. Cut off in hostile territory without a supply line, Hannibal would have required enormous quantities of fodder and considerable time to restore the fat reserves his elephants had used.

The researchers propose that he may have stopped bearing that cost after the elephants had served their purpose. There was little reason for an army already under extreme strain to feed expensive animals it could no longer deploy.

New evidence resolves an old debate

The study provides a means of assigning real figures to a march that nobody recorded in detail. Today, the same energy-landscape approach is used to examine how animals travel across difficult terrain and to design wildlife corridors that avoid exhausting ascents.

When applied to a campaign 2,200 years ago, it produces a clear result: the Traversette was the least costly way across the Alps.

The elephants were physically suited to surviving the route, while the most difficult struggle for Hannibal’s herd began only after the mountains lay behind them.