The Battle of Cissa was part of the Second Punic War. It was fought in the fall of 218 BC, near the town of Tarraco in north-eastern Iberia. A Roman army under Gnaeus Cornelius Scipio Calvus defeated an outnumbered Carthaginian army under Hanno, thus gaining control of the territory north of the Ebro River that Hannibal had just subdued a few months prior in the summer of 218 BC. This was the first battle that the Romans had ever fought in Iberia. It allowed the Romans to establish a secure base among friendly Iberian tribes, and due to the eventual success of the Scipio brothers in Spain, Hannibal looked for but never received reinforcements from Spain during the war.
Strategic situation
Hannibal's overland invasion of Italy was a highly risky venture, failure of which might have cost Carthage the war sooner, but he was forced to choose this strategy given the strategic limitations the Carthaginian empire faced in 218 BC, and this strategy had a better chance of succeeding than a seaborne invasion. Although sailing to Italy might have been faster and free from the hazards of a land march, at sea the entire fleet might be lost in a storm, and Roman naval dominance increased the risk to Hannibal's large armada, as it risked suffering crippling losses from Roman naval attacks despite Carthaginian warship escorts. Fleets normally sailed along the coast and beached at night or after every 2–3 days for victuals, yet Carthage had no bases on the coast between the Balearic Islands and Italy, which were dominated by Roman ally Massalia and her colonies and wild Ligurians, and Rome also controlled Sardinia, Corsica and Sicily, thus effectively dominating the coast between Spain and Italy, so making a seaborne invasion more dangerous than a land one. Moreover, enough horse transports to carry 9,000 horses to Italy might not have been available for Hannibal. An overland invasion, in contrast, would have the added advantage of achieving surprise.
Hannibal needed to time his movements carefully to keep the Romans in the dark, for if the Romans got hint of his intentions, they had enough recourses to fight a multi-front war: they could send one army to block the Carthaginian army at the Pyrenees, station a strong force in Cisalpine Gaul, and invade Africa with another simultaneously; or stand on the defensive with overwhelming forces in North Italy. After the successful conclusion of the Siege of Saguntum, Hannibal did nothing to provoke the Romans; he dismissed his army and did not immediately march for Italy in the Spring of 218 BC after he received the news of war. He spent the months of March – May strengthening the defense of Spain and Africa by garrisoning these areas, which were not threatening to Roman mainland— serving a dual purpose: along with securing the areas against the expected Roman invasion, it also reinforced the Roman perception that Carthage would fight a defensive war along the lines of the First Punic War, so Hannibal's overland invasion caught Rome off guard.
Carthaginian deployments
Hannibal stationed Hasdrubal Barca, his younger brother at the head of 12,650 infantry, 2,550 cavalry (11,580 African infantry, 300 Ligurains, 500 Balearic slingers, 450 Liby-Phoenician 300 Spanish Ilergetes and 1,800 Numidian cavalry from Masaesyli, Massylii, Mauri and Maccoei tribes) and 21 elephants to guard the Carthaginian possessions south of the Ebro. and sent 20,000 Iberian soldiers to Africa (including 13,850 infantry and 1,200 cavalry from the Mastiani, Thersitae, Olcades and Oretes tribes, and 870 Balearic slingers), and 4,000 soldiers garrisoning Carthage itself, probably between March -May. Hasdrubal and Carthage could raise additional soldiers if needed to fight Romans, and Carthage was unlikely to fall to a singular consular army in a few months.
Hannibal left Cartagena probably in late May or early June, timing his departure to allow the spring flooding of Spanish rivers to subside, ensuring the availability of food and fodder along the way, and after receiving envoys from Gallic tribes from the Po valley, who assured him of their willingness to cooperate against the Romans. Hannibal's army consisted of either 90,000 infantry and 12,000 cavalry, or 77,000 infantry and 10,000 cavalry, or with 26,000 infantry and 10,000 cavalry, and 37 elephants. The elephants were reported by Appian; there is no mention of the elephants by Polybius or Livy, so it has been speculated that the elephants may have been carried to Emporiae by sea. The Iberian contingent of the Punic navy, which numbered 50 quinqueremes (only 32 were manned) and 5 triremes, remained in Iberian waters, having shadowed Hannibal's army for some way. The army probably marched in smaller columns along a 5–7-mile (8.0–11.3 km) long stretch and the 290 mile march to the Ebro, during which they crossed the Sucor river and five major streams was uneventful, and the river was reached in the middle July.
Roman preparations and strategy
Rome expected Carthaginians to fight a defensive war, as Hannibal had anticipated, and they planned to attack both Spain and Africa, the only aggressive move they expected from Carthage was some form of attack on Sicily and they did not expect an overland attack. The Roman strategy was for Scipio was to set off first, engage Hannibal either north of the Ebro or east of the Pyrenees or the Rhône, where he may receive aid from Iberians or Gauls, and after Scipio had located and engaged Hannibal's forces, Sempronius, who would be stationed in Sicily, would invade Africa. Carthage was a strong city that would have to be blockaded for several months before it starved, also relief armies had to be beaten off during the time but since 241 BC, Rome had not negotiated but always dictated terms to Carthage, which had always backed down, so the Romans probably expected that Carthage was now bluffing by refusing to accept Roman terms and would capitulate as soon a Roman army blockaded the city, or roused the Numidians and Libyans to rebel against Carthage and decisively defeat Carthage. Carthage came close to capitulation in 256–55 BC when Marcus Attilus Regulus invaded Africa and if Scipio could keep Hannibal away from Africa long enough Sempronius could repeat the feat by making Carthage agree to terms or the political opponents of Barcids, some of whom had relations with Roman senators might assume power or trigger the recall Hannibal and accept Roman demands.
The Roman navy had been mobilized in 219 BC, fielding 220 quinqueremes for the Second Illyrian War. Consul Tiberius Sempronius Longus received 4 legions and instructions to sail for Africa with 160 quinqueremes. Publius Cornelius Scipio received 4 legions and was to sail for Iberia escorted by 60 ships.
Delay of Scipio
The Consuls took office in March and began organizing their forces, however, before Scipio's army was ready, the Boii and the Insubres, two major Gallic tribes in Cisalpine Gaul (modern northern Italy), antagonized by the founding of several Roman colonies on traditionally Gallic territory, and perhaps enticed by agents of Hannibal, attacked the Roman colonies of Placentia and Cremona, causing the Romans to flee to Mutina, which the Gauls then besieged. This probably occurred in April or May of 218 BC, the Roman Senate prioritized the defense of Italy over the overseas expedition, and Praetor Peregrinus Lucius Manlius Vulso marched from Ariminum with 600 Roman cavalry, 10,000 allied infantry and 1,000 allied cavalry, detached from Scipio's army, towards Cisalpine Gaul to aid the besieged Romans.
The Army of Manlius marched from Ariminum towards Mutina, and was ambushed twice on the way, losing 1,200 men and six standards, although they relieved Mutina, the army fell under a loose siege a few miles from Mutina at Tannetum. The Roman Senate now took one Roman and one allied legion (10,000 men) from the army of Scipio again and sent it to the Po valley under the command of Praetor Urbanus Gaius Atillius Serranus. As Atillius neared Tannetum, the Gauls retired without battle, and the Romans spent the summer of 218 BC recovering and fortifying Placentia and Cremona, probably in a two month long operation.
Sempronius remained in Rome until June/July, his army acting as a strategic reserve should more troops be needed in Cisalpine Gaul, Rome did not respond to the Carthaginian naval raids against Sicily and Lipari. Hannibal's passivity and non-threatening defensive dispositions during March – May probably influenced this decision by reinforcing the Roman perception they were fighting a repeat of the first war and the initiative lay with them. The Romans did not believe Hannibal would invade Italy, when they received news, probably in July, that Hannibal had crossed the Ebro, they probably assumed Hannibal's Catalonia campaign was part of securing Spain by subduing pro Roman tribes and creating a forward base. The Senate did not change the plan, Sempronius moved his forces to Sicily as planned while Scipio continued his preparations, to intercept Hannibal in Gaul. As a result, the departure of Scipo was delayed by two to three months.
The trans-Ebro Campaign
While Scipio raised new troops in Italy, the Carthaginian army crossed the Ebro River unopposed, in three columns: the northernmost detachment crossed at the confluence of the Ebro and Sicoris River and then proceeded along the river valley into the mountain countries, the central column crossed the Ebro at the oppidum of Mora and marched inland, the main column under Hannibal, along with the treasure chests and elephants, crossed the Ebro probably at the town of Adeba, and proceeded directly along the coast through Tarraco, Barcino, Gerunda, Emporiae and Illiberis. The separate detachments marched in such a way as to provide mutual support if needed, and the coastal detachment under Hannibal was also tasked with countering any possible Roman intervention. The area bordered Rhoda and Emporiae, colonies of Roman-allied Greek Massalia, so some of the neighboring tribes may have been pro Roman due to their influence.
Hannibal spent the months of July and August of 218 BC crossing the two hundred miles from the Ebro River to the Pyrenees, conquering the area by campaigning against the “Illurgetes” (perhaps not the Ilergetes at Lleida who were pro Carthaginian, but probably another obscure tribe between Tarraco and Barcino), the Bargusii at Serga valley, the Ausetani between Ausa (Vich) and Gerona along with the Lacetani, the Aeronosii, and the Andosini tribes. Hannibal stormed a number of unspecified cities and this campaign aimed to subdue region as quickly as possible, leading to heavy Carthaginian casualties. After subduing the Iberian tribes but leaving the Greek cities unmolested, Hannibal reorganized his army. A general named Hanno, who has been identified by various authors as Hannibal's nephew (son of Hasdrubal the Fair), a brother, or no Barcid relation, garrisoned the newly conquered territory north of the Ebro with 10,000 infantry and 1,000 cavalry, and based himself specifically to watch over the Bargusii, a pro-Roman tribe. Hanno also guarded the communication line with Hasdrubal Barca, and the heavy baggage left by Hannibal near a camp at Cissa.
Hannibal next released 3,000 Carpetani soldiers, along with 7,000 other warriors of dubious loyalty, so the Carthaginian army now numbered 50,000 infantry and 9,000 cavalry and 37 elephants. The Carthaginian detachments next crossed the Pyrenees Mountains into Gaul and regrouped at Illiberis in early September of 218 BC. They probably avoided the coastal road, as it contains many forested gorges and moved either through the Col de Banyuls or Col du Perthus or Col de la Perche, avoiding the Greeks in the coast altogether.
The trans-Ebro campaign allowed Hannibal to give his new recruits valuable combat experience, and impress upon the Iberian tribes the extent of the power of Carthage, especially those which might have been influenced by the Greek colonies of Massalia, which were not captured, and his shedding of unwilling troops and heavy baggage allowed him to form a more mobile, streamlined, loyal, battle-hardened experienced army, also reduce his supply and provisioning burden by decreasing the number of soldiers, pack animals and size of the baggage train. Hannibal probably now abandoned any thoughts of fighting the Romans, as the season was getting late, and focused on quickly reaching Italy.