It’s one of military history’s most exciting chapters. In 218 BCE, Carthaginian general Hannibal crossed the Alps with a squadron of 37 war elephants to invade Italy.

While we can’t say which route he used to cross this rugged terrain, a new study published today in the journal Proceedings of the National Academy of Sciences (PNAS) offers some new clues. The new analysis shows which of Hannibal’s potential routes would have been less taxing on his 40,000 men, 7,000 horses and 37 war elephants. His best option likely would’ve been the Col de la Traversette, a pass with an altitude of 9,669 feet on the border between Italy and France.

Why did Hannibal cross the alps?
Hannibal hailed from Carthage, a dominant ancient Phoenician city-state and empire in present-day Tunisia. During the Second Punic War, Carthage controlled North Africa’s coast and the Iberian peninsula (present-day Spain and Portugal). Rome sought to use its naval dominance to force its rival to surrender.

To bring the war right to Rome’s doorstep, Hannibal led his army over the Alps from France into Italy. This was easier said than done, as it required traversing rugged terrain, snow, and ice, while surviving mountain passes that were controlled by local tribesmen who could attack them from above. However, going through the mountain range meant he could avoid Rome’s fearsome navy on the Mediterranean and its army garrisons on land.

Only two primary sources of the event survive and were written 20 and 160 years after the event. And since no archaeological evidence is available, interpreting the events of the crossing is difficult. All modern theories depend on interpreting the three place names used by the writer Polybius (Island, Skaras, and Allobroges) and the wider range of tribe and place names written by Livy. Scholars then compare those locations with current geographical knowledge.

According to Livy’s account, Hannibal marched his army across the Alps in just 16 days. However, Hannibal’s entire military campaign took over roughly two months and ended up being very costly. Hannibal lost upwards of 20,000 men and Carthage ultimately lost the war.

Why he used elephants for the crossing is still unclear. He may have intended them to provide a tactical element of surprise during his first battles against the Romans. He also may have hoped that the wonder of seeing these elephants may help him help recruit the Celts of Northern Italy to his side.

Saving energy
In this new study, a team from the University of Oxford in the U.K., the German Centre for Integrative Biodiversity Research (iDiv), and Friedrich Schiller University Jena in Germany evaluated the competing theories about which route over the mountains Hannibal took. Previously, historians believed that he may have taken the Col du Clapier, an 8,127 feet-high mountain pass between Savoy, France, and Piedmont, Italy.

The team used route modelling and elevation data, to estimate the energy cost of each possible Alpine crossing. They used data collected on how much energy modern African elephants would use to make a crossing like this, based on their body mass and the terrain.

Their results suggest that the Col de la Traversette would have been both the shortest and most energetically efficient route. When compared to the Travesette route, traveling via the Col de Montgenèvre would have required 11 percent more energy. Col du Clapier would have required 16 percent more, while Col du Mont Cenis needed 19 percent more energy.

The team’s models also underscore what a physical challenge it was to move an army (and elephants) through the mountains. If they took the Traversette route, the men would have lost 19 percent of their body fat reserves, which may be one factor behind the high human mortality rate later in battle. Hannibal lost roughly 20,000 men by the end of the campaign.

Surprisingly, the new analysis suggests that the war elephants would have fared better on the crossing. Elephants would have only lost four percent of their fat reserves, based on the team’s models. These high energy reserves likely explain why many, if not most, of the elephants survived.

“The question of Hannibal’s exact route has been debated for generations,” Dr. Emilio Berti, a study co-author and biologist at the German Centre for Integrative Biodiversity Research and the Friedrich Schiller University Jena, said in a statement.

“The new analysis does not eliminate all ambiguity, but it does strengthen the case for the Traversette route by demonstrating that it would better accommodate the demands of moving a large army that included elephants through extremely difficult alpine terrain.”