It was one of the most outrageously bold manoeuvres in military history - and 2,000 years on experts are still trying to work out how he pulled it off.

But now the mystery of how Hannibal's army managed to catch the Romans off guard by crossing the Alps in an improbable 1,000-mile march could be solved, it is claimed, by tracking a trail of dung.

Scientists say that a thin crust of ancient excrement left by Hannibal's animals, which famously included 37 elephants, could reveal the route the legendary Carthaginian general took.

Hannibal's 30,000-strong army trudged through deep snow in the grip of winter in 218BC with more than 15,000 mules and horses before crossing into Italy where they nearly made it to the gates of ancient Rome.

But, according to experts, such a large movement of men and animals must have left what they describe as a "mass animal deposition event".

And at a patch of swampy ground near the Col de la Traversette, a narrow pass between Grenoble in France and Turin in Italy, they think they have found it in an unusual layer of muck about 16in beneath the surface.

In a blog post, Chris Allen, a senior lecturer in environmental microbiology at Queen's University Belfast, said: "Using a combination of microbial genetic analysis, environmental chemistry, pollen analysis and various geophysical techniques, we unveiled a mass animal deposition of faecal materials – probably from horses – at a site near the Col de Traversette.