After turning north with his army column into the gradually narrowing Rhône Valley, Hannibal left behind sunny Provence. By the time the path through Gaul approached modern Montélimar on the Rhône, the distant jagged peaks of the Alps could be glimpsed from time to time eastward, especially up the Val Drôme where the Drôme River comes in. During the four-day march, Hannibal encountered little resistance from the Celts, but this does not mean that they were not watching his progress carefully. If anything, these Celts were not interested in delaying a hungry army that would overrun their farms, deplete their resources, or worse.1 Hannibal may have purchased food provisions from time to time, distributing some Punic silver rather than risk a fight from bands of gathering Celtic warriors. He did not want anything to slow his progress by now.
September had come, and the leaves of deciduous trees that had been turning golden yellow were accompanied by increasingly cooler nights. Fall winds began to strip the trees, and more and more bare branches showed along the way. Stream waters to be crossed, however depleted by decreased runoff, were now considerably colder than when the army had started in Spain’s summer.
The army paused in a low and fertile plain that formed a vast triangle where the fast Isère flows into the Rhône from the east.2 This river junction was the traditional tribal boundary of the populous Allobroges for centuries3 and in 125 BCE Romans would confront a combined army of Allobroges and Arveni from the Central Massif. Hannibal’s army now encountered the Allobroges, the largest Celtic tribe yet, one whose territory stretched much of the way along the Rhône north of the Isère. One center of the Allobroges was near what would become Geneva, Switzerland; another was near modern Grenoble.4 This part of Gaul between the Rhône and the Isère was most likely the delta region Polybius called “the Island.”5 Immediately to the east of the Rhône and south of the Isère, the Pre-Alps massifs begin to ascend to the northeast.6 The Alpine pass route and the ultimate summit that follows—not the only reasonable possibility for the march—nonetheless aptly fit the difficult terrain and challenging high altitude for the conditions Hannibal’s army encountered, according to Polybius.
At this time, two chieftain brothers had a leadership dispute about which of them should be the king. Apparently only the eldest brother cautiously sent a peaceful delegation to meet Hannibal, making a personal overture to him to assist in placing him on the throne. Whether the younger brother also reached out is unknown, as Polybius does not say. But Hannibal agreed to this apparently sensible request: by a show of force, he drove away any supporters of the younger brother who were present.
In visible gratitude, the new chief of the Isère lowland plain supplied Hannibal’s army with much-needed provisions of ample food, fresher weapons, and warmer clothing for the journey approaching colder weather, including thick leather shoes.7 Hannibal’s army was also grateful for an armed guard from the chief marching at its rear.
This eastward passage of the army along the Isère traversed some of the richest farm country in Gaul, with farms that were also plentiful in cattle. Harvests were stored in the Celts’ wooden barns. Nearly all farming had stopped for the fall, as the last edible tubers and roots were dug out of the ground and stored carefully in cellars. Because this is fertile land, the elder brother could afford to sell to Hannibal or give him ample surplus agricultural bounty. Not so the brother to the east, whose territory lay within the mountain valleys, a far more rugged land.
On the south side of the Isère River, the brooding massifs approach closer and closer in the formidable, thickly wooded Vercors Pre-Alps that rise nearly vertical only a few miles from the river canyon. About this land, Polybius commented, “[H]ere the baseline is formed by a range of mountains difficult to climb and, one may say, almost inaccessible.”8 The impenetrability of the Vercor massifs was borne out during World War II, when the famously tenacious Vercor French Resistance proved impossible for the Germans and the Vichy government to root out. This was the mountain territory of the other Allobroges brother. Hannibal may have second-guessed his earlier decision, but it was too late if he wanted to advance eastward here.
Just to the north, outside of modern Grenoble, are the twin bluffs of the towering “Gateway to the Alps,” where the Isère River bursts through the mountains from narrow valleys upriver.9 The Vercors Massif rises on the southwest, and the Chartreuse Massif rises on the northeast side of the narrow Isère. Rising abruptly on average more than two thousand spectacular feet from the river canyon that is just under six hundred feet in elevation, these massif ridges look literally like a huge broken wall. Here the Isère River pours out of the mountains.
This is the narrowest canyon of the lower Isère. The only easy passage is squeezed into an alluvial valley, full of sediment from floods, alongside the river: an opening no wider than three-quarters of a mile and shared by the river. Anyone would have sensed danger here—especially the acutely pragmatic Hannibal—and trouble was not long in coming. Unfortunately for the Carthaginians, their lowland Allobroges allies would go no farther and returned homeward.10 They knew Hannibal’s predicament and knew also how they themselves would be received here by their now-aggrieved kinsmen.
Control of this natural gateway lay completely in the hands of the mountain Allobroges, who may have had their fortress just above modern Voreppe, one plausible ambush place that fits what Polybius tells us. It had ample watch points along the ridge from which one could view any movement in all directions along the valley below.11 The only feasible pathway lay immediately under their noses at the base of the bluff plateau on the north side of the Isère Valley. Hannibal’s scouts reported back to him that this pathway was not only watched by armed men above but also that they made clear their intentions that they would oppose his army’s passage.
However, Hannibal’s Celtic guides also informed him that the Allobroges had left their vantage posts and gone to their fort and nearby homes for the night, thinking Hannibal would not possibly advance after dark. A night sally by anyone, especially strangers unfamiliar with the steep terrain, would be completely unconventional. Hannibal, however, was always unconventional, as the Romans would also discover to their misfortune. He carefully set his plan to foil the Allobroges at their own game of launching an ambush from higher ground. One wonders how much Hannibal had learned about raids and ambushes from the Celtiberians in Spain as well as in Gaul, where opportunistic Celtic raids were a common maneuver.12 Hannibal would later employ similar raids and ambushes on the Romans with great success.
Hannibal left the bulk of his army camped below with their fires burning as usual to lull the enemy and formed a contingent of his best men, which he led himself to climb up to the narrowest path and take over the Celts’ watch posts by night. Leading the way always endeared him to his soldiers, who saw that he took the same risks they did. They recognized that he would not order anyone to do what he was unwilling to attempt himself. Hannibal’s men took over every one of the Allobroges’ watch points above the guarded road.
Daylight came, and the surprised Allobroges found that all of their control points were occupied by Hannibal’s men. They probably would have given up had they not seen that Hannibal’s long train of soldiers, who had to march in narrow file due to the terrain was accompanied by pack animals carrying the greatest amount of supplies they had ever imagined, laden and crawling slowly along the valley. This veritable cornucopia of an army’s provisions overcame the Allobroges’ initial hesitance over being outsmarted. They rushed en masse from their fortress—a typical Celtic battle maneuver of “all or nothing” in a headlong “frenzied assault” as Stephen Allen puts it13—to attack the long column exactly where the pack animals were thickest and least protected by soldiers. It was pandemonium for the narrowly constricted army, usually disciplined but nearly trapped here.
Even though Hannibal expected something like this, the ambush was horrible at first for his army, as many animals and men were casualties of both the Allobroges marauders and the steep path. Wounded army horses rushed pell-mell in both directions up and down the path and knocked many other pack animals off the route into the dense shrubbery on the steep hillside where the Celts stripped them of their goods and killed their drivers.
Alerted by the screams of men and animals, Hannibal realized that he could lose his entire provisions. He brought back all his men who had been guarding the route from higher ground above. Some were sent down into the Celts, many of whom scattered with their stolen goods, while other warriors were ordered to the head of his column, where the fighting was fiercest. Although he soon routed the Allobroges, his soldiers chasing them in all directions into the woods, it was at some material cost. Hannibal lost quite a few men and animals. A lot more pack animals laden with supplies were unaccounted for at first, having fled in terror. However, his men slowly collected them, and his army resumed its march over the most dangerous narrows until all emerged in the broader Isère river valley under the high ridges.
But Hannibal also took the nearly empty Celtic fort, since its Allobroges inhabitants had fled to the surrounding countryside, and here he not only recovered the remainder of his pack animals that had not been butchered in the battle but also took all the food supplies that the Allobroges had harvested for the coming winter. In addition, he took their abandoned cattle, which they normally kept within their walls when under siege or at war. The Celts’ reports of Hannibal’s success and the losses of the Allobroges were such an effective propaganda tool that none of the other tribes dared attack Hannibal’s army as they wound their way up into the mountains.
Hannibal seems to have turned away from the Isère and instead would have followed the ancient established Maurienne trade route of the Celts in the Arc River Valley—another demarcation point of different Celtic mountain tribes, as is true of so many Alps watersheds. His scouts must have informed him of this historic route. As the news about the Allobroges’ losses spread to successive Celtic hamlets and towns, no one harassed the army for four days,14 although these smaller tribes must have looked longingly at the uncountable wealth slowly passing by in both animals and the piled goods they carried.
The autumn weather in the mountains was turning increasingly cold. Darkening clouds now heavy with freezing rain, hail, and even sleet forced the army to slog over ground that was frost covered when they woke in the morning. It was now moving toward late October, and when the clouds lifted, the men crowded together around campfires could see that the mountain peaks above the tree lines were white with heavy snow. Every soldier and Hannibal himself must have wondered at night how much farther the army had to go and how high the army had to ascend to reach the frontier of Italy. But Hannibal quietly inspired his men by his own sacrifices. Instead of demanding special comforts befitting his rank as Carthaginian nobility and their general, Hannibal slept humbly on the hard ground just like his tough soldiers, wrapped only in a few heavy blankets. This fact—possibly intended to emulate a young Alexander the Great—would be remembered forever by his and other armies and later recorded by his duly impressed enemies. Everything Hannibal did had at least one strategic purpose and likely was layered with deeper intent to breed loyalty. But this quality would soon be tested in the high Alps towering just above the army.