Elephants in the Alps
Hannibal of Carthage led his army over the Alps to attack Italy during the Second Punic War, in 218-201 BC. Hannibal's forces famously included elephants, plus thousands of horses and mules.
2200 years later, their droppings trace the army's path through the mountains. The scientists talk about "clearly bioturbated deposits with fecal chemical biomarkers and microbial signatures". Informally, it's signs of a lot of poop and stomp and poop and stomp and ...
Hannibal's army traveled along the Mediterranean coast of today's Spain and France, then inland and up through the Alps to reach Italy and attack the Roman forces. The army included 30,000 men, 37 elephants, and over 15,000 horses and mules. That's a lot of feces. But enough to be detected over 2000 years later? Yes. Let's see how they discovered this.
How Do You March Elephants from France to Italy?
Historians agree that Hannibal's army traveled along the Mediterranean coast of Iberia and southern Gaul, and then turned north to follow the Rhône river north to a point near today's city of Valence. Then they turned east and crossed the Rhône in late September of 218 BC. They then made their way through the Alps as quickly as possible, as winter was coming. Daily snowfall was increasing as they came through the last pass at the end of October. From there they made their way down to the Po river valley, where they attacked the Taurini people's settlement. A Roman colony was established there 191 years later, in 27 BC, called Castra Taurinorum and later Julia Augusta Turinorum. This became today's Torino (or Turin) in northwestern Italy.
But which route did Hannibal's army follow from the Rhône river through the Alps?
Did they turn off the Rhône to follow the Drôme river, or did they continue a little further up to Rhône to then turn east along the Isère river? And then, how did they make their way through the mountains?
The precise route has been debated since ancient times. No physical artifacts like coins, metal buckles, or other pieces of clothing or equipment have ever been found along any of the potential routes. We only have some sketchy and contradictory reports from early historians. They describe the passage through the Insula area vaguely. The army crossed the Rhône, traveled east up a tributary river, then through a pass into the mountains. But which river?
And which pass?
The closer you look, the more complicated it becomes. Historians have only narrowed it down to three main routes through the Alps. But even among those agreeing on one of those three routes, the precise details are still a matter of debate.
Now, research in the early 2010s may have found the invasion route. They discovered a large area of churned up soil contaminated with a unusually large amount of animal feces.
The Fecal Trail
Transhumance is the seasonal movement of people along with their livestock, moving between fixed summer and winter grazing areas. There is evidence of transhumance in the Alps going back to about 3000 BCE during the late Neolithic period. All current Alpine pastures are below 2800 meters, and most are below 2400 meters. However, there is evidence for some pastures above the treeline during the Bronze Age, in the 17th to 11th centuries BCE. Ancient domesticated animal droppings in the mountains might be from early herders.
We need to consider scale. Elephants are large. African elephants weigh from 4000 to 7000 kilograms, and stand 3 to 4 meters tall. How much do elephants poop?
People have studied this! An elephant produces about 110 kg fecal output per day3,4, defecating every 1.4-1.9 hours3. As for urine, it's 25-53 liters of urine per day1,2,4,5,6, with an average volume per urination of 5.5 liters, and a maximum volume of 10.6 liters1.
1 Benedict, F.G., 1936,
The physiology of the elephant,
Carnegie Institution of Washington, Washington, pg 200.
2 Cheeran, J.V., 2002, Elephant facts, Journal of Indian Veterinary Association Kerala 7(3):12-14.
3 Coe, M., 1972. Defaecation by African elephants (Loxodonta africana africana (Blumenbach)), East African Wildlife Journal 10:165-174.
4 Dutta, D., 2003, Physiology of elephant, In Das, D. (editor), Healthcard, Breeding and Management of Asian Elephants, New Delhi Project Elephant, Government of India, pp 17-22.
5 Simon, K.J., 1958, A preliminary study of the urine of elephants, Indian Veterinary Journal 35:345.
6 Simon, K.J., 1959, Further studies on the urine of elephants, Indian Veterinary Journal 36:209-212.
A typical 450 kg horse produces about 20-25 kg of feces per day, in 10 to 12 droppings, plus about 5.6 to 7.7 liters of urine. I don't have any handy number for a mule's average daily output of feces and urine, nor for the horse-to-mule ratio within Hannibal's army, so let's use 20 kg of feces for both horses and mules.
An elephant produces a lot of feces, both per dropping and per day, and no one but Hannibal has ever marched 37 elephants through the Alps. However, the number of horses and mules overwhelms the elephant output.
37 elephants at 110 kg each yields 4070 kg of elephant feces per day.
15,000 horses and mules at 20 kg each yields 300,000 kg of feces per day. So those 37 elephants contributed less than 1.5% of the total animal fecal output of Hannibal's army.
History and Physical EvidencePart II Part I
The research is described in a two-part paper by an international team: "Biostratigraphic evidence relating to the age-old question of Hannibal's Invasion of Italy", published in Archaeometry in 2016. Part I is: "History and geological reconstruction", and Part II is: "Chemical biomarkers and microbial signatures",
They looked at an alluvial floodplain mire, an area where sediment has eroded and washed down into a relatively flat area. This site is about 2580 meters above sea level. It's just below the Col de la Traversette, a pass at about 3000 meters elevation on today's border between France and Italy. That means that the army followed the southernmost of the three possible routes, passing through the Col de la Traversette on the north slopes of Monte Viso, and following the Po from its source. Monte Viso is the highest mountain of the Cottian Alps, about 500 meters taller than the surrounding peaks.
They found a large area with a layer they described as a bioturbated MAD. That is, a churned-up Mass Animal Deposition bed. The ancient descriptions list distinctive landmarks: a "certain bare rock", a deep gorge on the approach to the final and highest pass, a bivouac area near that pass where they could rest and reorganize, and a "view into Italia" from the pass and just beyond.
The authors of the 2016 paper believe that they found that bivouac area.
Smithsonian magazine ran a popular article about the study in 2017, as did Vice.
The Greek historian Polybius of Megalopolis interviewed survivors some 60 years after the invasion in order to write his Histories. Polybius describes a two-level rockfall below the final pass. This led to a search of potential routes, with rockfall debris below the Col de la Traversette at 2600 meters providing the best match to the description.Histories
The Roman historian Titus Livius, known in English as Livy, wrote Ab Urbe Condita or the History of Rome. He may have used a first-hand account from a member of Hannibal's party. Livy says that the two-level rockfall was such an obstruction that Hannibal had firewood carried to the site so the larger boulders could be broken by the heat of fire and moved out of the way.
The ancient accounts also described frozen ground. True permafrost probably didn't exist near the surface then, but the Col de la Traversette is the only mountain pass within the snowline at about 2800 meters. The frozen ground probably refers to patches of permanent snow cover.
Of course, there had to be foraging plants for the animals and enough watering holes for both animals and men.
The site is at 44° 42.588' N, 7° 03.281' E. It is a gently sloping area of basalt covered with about a meter of organic-rich, alluvial mire. The nearby Guil River headwaters periodically flood the site. This makes it one of the few nearly level areas with water and grasses and sedges for foraging.
The churned-up MAD layer is about 45 centimeters below current ground level. Carbon 14 analysis places some of this during the time of Hannibal's invasion.
The amount of churning (or bioturbation) is much more than usually seen in bog cores in alpine settings or other areas. The organic content within this layer is higher than anywhere else below the surface. This carbon-rich layer is darker black.
The Pollen in the Poop
A variety of pollen was found throughout the soil layers. The MAD layer contains a distinct spike in the amount of pollen from Cyperaceae, flowering plants called sedges. Animals prefer to eat true grasses rather than the similar-looking sedges, but sedges dominate alpine meadows like this site.
The spike in sedge pollen in the MAD layer may be from pollen grains passing through the digestive systems of grazing animals.
Feces contain some distinctive stanols and bile acids. These were found in the soil at the site, but not in the surrounding region. The concentration peaks within the churned-up layer.
5β-stigmastanol is commonly used as a biomarker for ruminant animals. It is also the most abundant stanol in horse feces.
Deoxycholic acid (or DCA) is a secondary bile acid found in animal feces.
The Bacteria in the Soil
They also collected and analyzed the micro-organisms in the soil. Many of the bacteria from the churned-up layer were Clostridium. They normally make up only 2-3% of the bacterial population in soil, but they were above 12% of the bacteria in that layer. Clostridium make up over 70% per cent of the microbes in horse manure. They are very stable in soil, surviving for thousands of years. That makes them especially dangerous, as some are deadly pathogens. Clostridium histolyticum excretes collegenase, which eats through animal tissue. Clostridium botulinum creates the lethal neurotoxin used to manufacture Botox. Other strains cause gas gangrene.
The abundance of endospore bacteria from mammal digestive systems can only be explained by the passage of at least hundreds to thousands of animals, far more than would be involved in tribal trade at that time.
So, Are We Certain It Was Hannibal?
There is uncertainty in the carbon 14 dating, and the churning itself makes sampling within that layer uncertain. But there definitely was some army-sized group of animals that passed through that site around the time of Hannibal's invasion. It could have been another similar group, but history doesn't tell us of any alternatives.
Hannibal's army looks like the best explanation for what they found.