The Romans, under Gnaeus Scipio, had invaded Iberia in late 218 BC and established a foothold after winning the Battle of Cissa.

Hasdrubal attempted to evict the Romans in 217 BC, but this ended in defeat when the Carthaginian naval contingent was mauled at the Battle of Ebro River.

Hasdrubal lost the opportunity to reinforce Hannibal when he was at the peak of his success and an army that was ready to sail to Italy was diverted to Iberia.

This effect on potential reinforcements for Hannibal has caused the historian Klaus Zimmermann to state “the Scipios' victory ... may well have been the decisive battle of the war”.

[22][23] Polybius considered this act of bad faith by the Romans to be the single greatest cause of war with Carthage breaking out again nineteen years later.

[25] Carthage gained silver mines, agricultural wealth, manpower, military facilities such as shipyards and territorial depth which encouraged it to stand up to future Roman demands.

[34] Meanwhile, Hannibal assembled a Carthaginian army in New Carthage (modern Cartagena) and entered Gaul, taking an inland route to avoid the Roman allies along the coast.

[39] The Carthaginians crossed the Alps[35] early in 217 BC, taking the Romans by surprise and causing them to cancel their main campaign planned for the year, an invasion of Africa.

[40] Gnaeus Scipio continued on from Massala to Iberia, landing his army of four legions, two Roman and two allied —approximately 25,000 men— in the autumn of 218 BC at Cissa and winning support among the local tribes.

The naval component was defeated by 55 Roman and Massalian vessels at the Battle of Ebro River, with 29 Carthaginian ships were lost.

[39] The Roman lodgement was preventing the Carthaginians from sending reinforcements from Iberia to Hannibal or to the insurgent Gauls in northern Italy.

Hasdrubal received orders from Carthage to move into Italy and join up with Hannibal to put pressure on the Romans in their homeland.

[43] The historian of the Punic Wars Dexter Hoyos points out this was “even though [Iberia] itself was supposed to be a reservoir of first-class fighting men.” Clearly the enthusiasm for Carthage of the indigenous Iberians was suspect.

[43] Having quelled the Turdetani, Hasdrubal left his subordinate Himilco in charge at Cartagena and marched north with his field army in early 215 BC.

[44] Most male Roman citizens were liable for military service and would serve as infantry, a better-off minority providing a cavalry component.

Approximately 1,200 of the infantry, poorer or younger men unable to afford the armour and equipment of a standard legionary, served as javelin-armed skirmishers, known as velites.

[52][53] Iberia provided large numbers of experienced infantry; unarmoured troops who would charge ferociously, but had a reputation for breaking off if a combat was protracted.

[51] The Carthaginian army also had a small number of war elephants, perhaps the 21 which Hannibal left in Iberia when he set out for Italy in 218 BC.

At the Battle of Tunis in 255 BC, during the First Punic War, a line of Carthaginian elephants caused chaos among 13,000 Roman legionaries.

[64][50] Livy states the Iberians knew that victory would mean they would march with the rest of Hasdrubal's army to Italy and that their unwillingness to leave Iberia made them unenthusiastic fighters.

[50] Meanwhile, the strong blocks of North African and Poeni heavy infantry on either side of the Iberians partially turned and engaged the flanks of the two Roman legions.

[41] The shattered Carthaginian army retired to Cartagena, leaving the Romans firmly established in north-east Iberia and blocking the overland route to Italy.

[51] This was largely because the Battle of Cannae was fought in Italy at approximately the same time and turned out disastrously for the Romans; for several years they concentrated their manpower and resources on safeguarding their homeland, leaving nothing for Iberia.

[74] They would fight on in Iberia with varying results until 212 BC, when the Romans were heavily defeated at the Battle of the Upper Baetis and both of the Scipios were killed.

He raised an army which was meant to land at Locri in Italy in 215 BC, but was diverted to Iberia after the Carthaginian defeat at Ibera.

[65][78] The classicist Howard Scullard is of the opinion that the Romans' victory prevented them from being expelled from Iberia, not least because the Iberian tribes would have abandoned Rome; and prevented Hasdrubal from promptly marching at full strength to reinforce Hannibal in Italy, where “Rome could hardly withstand the double force.”[79] Klaus Zimmermann agrees: “the Scipios' victory ... may well have been the decisive battle of the war”[38]