Scientists in Ireland think they may have solved one of the great mysteries of ancient military history - what route Hannibal took crossing the Alps.

And the researchers at Dublin City University and Queen's University have done it, they claim, through the discovery of a big deposit of animal faeces.

Commander-in-Chief of the army of Carthage during the second Punic War with Rome between 218 and 201 BC, Hannibal secured his place in history for what considered one of the most daring military endeavours of the ancient past.

This is because he was responsible for leading 30,000 men, 37 elephants and 15,000 horses and mules over the Alps, in a move that brought the military forces of ancient Rome to their knees.

He went on to occupy large parts of Italy for 15 years, until a counter invasion in Carthage led to his defeat in Zama in 202 BC.

The events ultimately helped to sculpt the Roman Republic, and later the hugely important and influential empire.

For the 2,000 years since, it has been unclear what route Hannibal took to cross the treacherous Alpine peaks, as there was no archaeological evidence.

However, a multi-disciplinary team from Ireland, Northern Ireland, Canada, the US, France and Estonia thinks it may have solved the quandary using chemical evidence.

The scientists used a mixture of microbial metagenome analysis, environmental chemistry, geomorphic and pedological investigation, pollen analyses and various other geophysical techniques to identify the location of a mass deposition of animal faeces at a wet swampy area in the Alps.

An aerial photo of the expedition site, (Pic: Peeter Somelar of the University of Tartuu)

"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, " said  Dr Chris Allen from the Institute for Global Food Security at Queen's University Belfast.

"Over 70% 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."

The remnants of the ancient animal dirt were found near the Col de Traversette pass - a 3,000m high route in the upper Guil Valley near Mt Viso.

It was first proposed as being a possible point on Hannibal's journey more than 50 years ago by biologist Sir Gavin de Beer.

"The results constitute the first chemical and biological evidence of the passage of large numbers of mammals, possibly indicating the route of the Hannibalic army at this time," Brian Kelleher, an academic from our School of Chemical Science.

"Combined with the geological analysis, these data provide a background supporting the need for further historical archaeological exploration in this area."

The paper detailing the research has been published online in the journal Archaeometry.