Hannibal Barca had planned to invade
Italy overland from Spain, since Roman naval dominance of the
Mediterranean Sea made a sea-borne invasion impossible. The Romans expected Carthage to remain on the defensive, and Hannibal hoped that the invasion would catch them off guard and forestall the expected Roman invasions of Spain and Africa. The
Boii and
Insubres had agreed to meet Hannibal with provisions and reinforcements upon his arrival in Italy, when the Carthaginian army would be at its most vulnerable due to exhaustion and expected losses during the
Alpine crossing. After the war broke out in the spring of 218 BC, the Boii and Insubres, resenting Roman occupation of Gallic lands and perhaps incited by agents of Hannibal, attacked the Roman colonies of
Placentia and
Cremona, afterwards besieging
Mutina where the colonists had fled. This revolt, which probably occurred in April or May, would ultimately force Rome and Hannibal to change their respective war strategies.
Strategic consequences of the revolt Rome had mobilized two consular armies in 218 BC, they planned to send consul
Publius Cornelius Scipio with 4 legions (8,000 Roman and 14,000 allied infantry and 600 Roman and 1,600 allied horse) under the escort of 60
quinqueremes to Spain. Scipio was to engage Hannibal either north of the Ebro or east of the Pyrenees or on the Rhône, and after Scipio had occupied Hannibal's forces, Consul
Tiberius Sempronius Longus with 4 legions (2
Romans and 2 allied, 8,000 Roman and 16,000 allied infantry and 600 Roman and 1,800 allied horse) under the escort of 160
quinqueremes was to invade Africa and attack Carthage. This army was ambushed by the Gauls twice on the way, losing 1,200 men and six standards, and although they relieved Mutina, the combined Roman army then fell under a loose siege a few miles from Mutina at Tannetum. and the Romans spent the summer of 218 BC recovering and fortifying Placentia and Cremona. The army of Sepmronius, kept in Rome as a strategic reserve, left Rome in June or July for Sicily. Scipio was forced to raise and train new troops to replace the ones taken from him, which delayed his departure for Spain by two-three months. This delay, a direct consequence of the Gallic revolt, indirectly influenced the course of Hannibal's invasion of Italy.
Hannibal’s arrival in Cisalpine Gaul Hannibal after subduing Catalonia left Hanno with 11,000 soldiers to guard the area, further reduced his army, abandoned his heavy baggage, and focused on reaching Italy quickly, his streamlined army reached the Rhone in three weeks,
forced a passage across the river against Gallic resistance only to find Scipio's army stationed four days march to the south of his crossing site– another consequence of Scipio's delayed start from Italy. Hannibal chose not to fight the Romans, but he probably was forced to change his planned route across Alps due to the Roman presence, and his five-week crossing of the Alps using an alternate, more arduous route caused the loss of the majority of his pack animals and 12,000 to 20,000 irreplaceable, battle tested, loyal veteran soldiers, who might have augmented Hannibal's strength in Italy, another indirect consequence of Scipio's delayed arrival in Gaul. The Carthaginians found no supplies and reinforcements from the Gauls awaiting them after entering Italy, the Gauls joined the Carthaginians only after Hannibal defeated the
Taurini three days after reaching Italy. Hannibal wintered in Cisalpine Gaul after his victories in the battle of
Ticinus and
Trebia, and when he marched south in spring of 217 BC, more than half of his army consisted of Gallic recruits. ==Prelude==