The first battle probably took place on the Isère River between St. Quentin and the plateau of Montaud. The local tribesmen, the Allobroges, blocked the narrow pathway that Hannibal needed to cross between the mountains of Vercors and the Bec d'Echaillon. He could neither go over the mountains of Vercors, 4500 feet high, nor go around or across the Bec d'Echaillon, a precipitous cliff surmounted by two plateaus. Regardless of exactly where the battle took place, it was on a narrow passageway with impassable peaks on either side. Hannibal's Gallic guides, the Boii, had been sent to find out about the tribesmen and determine their intentions. They eventually found out that the hostile Allobroges wanted to block Hannibal's passage.
The Boii also told Hannibal that the tribesmen return to their homes at night, so Hannibal picked a force of his best light-armed infantrymen and that night, led them past the hostile tribesmen to the plateau of Montaud. In the morning, Hannibal's army advanced and the natives
