After the war Carthage expanded its holdings in Iberia where in 219 BC a Carthaginian army under Hannibal besieged, captured and sacked the pro-Roman city of Saguntum.

After the death or capture of more than 120,000 Roman troops in less than three years, many of Rome's Italian allies, notably Capua, defected to Carthage, giving Hannibal control over much of southern Italy.

The Romans took drastic steps to raise new legions: enrolling slaves, criminals and those who did not meet the usual property qualification; this vastly increased the number of men they had under arms.

[2][6][7] Modern historians consider Polybius to have treated the relatives of Scipio Aemilianus, his patron and friend, unduly favourably but the consensus is to accept his account largely at face value.

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.

[49] During this period of Roman expansion, Carthage, with its capital in what is now Tunisia, had come to dominate southern Iberia, much of the coastal regions of North Africa, the Balearic Islands, Corsica, Sardinia and the western half of Sicily.

[52][53] According to the classicist Richard Miles Rome's expansionary attitude after southern Italy came under its control combined with Carthage's proprietary approach to Sicily caused the two powers to stumble into war more by accident than design.

[60] Rome exploited Carthage's distraction during the Truceless War against rebellious mercenaries and Libyan subjects to break the peace treaty and annex Carthaginian Sardinia and Corsica in 238 BC.

[68] This gave Carthage the silver mines, agricultural wealth, manpower, military facilities such as shipyards, and territorial depth to stand up to future Roman demands with confidence.

[85] The Carthaginians reached the foot of the Alps by late autumn and crossed them in 15 days, surmounting the difficulties of climate, terrain[82] and the guerrilla warfare tactics of the native Ligurians.

Hannibal arrived in Cisalpine Gaul with 20,000 infantry, 6,000 cavalry and an unknown number of elephants – the survivors of the 37 with which he left Iberia[86][87] – some time in November; the Romans had already gone into their winter quarters.

[88] Shortly after arriving in Italy the Carthaginians captured the chief city of the hostile Taurini (in the area of modern Turin) and seized its food stocks.

One was stationed at Arretium and one on the Adriatic coast; they would be able to block Hannibal's possible advance into central Italy and were positioned to move north to operate in Cisalpine Gaul.

[106] The Carthaginians continued their march through Etruria, then Umbria, to the Adriatic coast, then turned south into Apulia,[107] hoping to win over some of the ethnic Greek and Italic cities of southern Italy.

The head of the embassy that was sent to Carthage right before the war broke out in 218 BC, Quintus Fabius Maximus, was elected dictator by the Roman Assembly and adopted the "Fabian strategy" of avoiding pitched battles, relying instead on low-level harassment to wear the invader down, until Rome could rebuild its military strength.

[109][110] Fabius was unpopular at this period with parts of the Roman army, public and the senate, for avoiding battle while Italy was being devastated by the enemy: there was awareness that his tactics would not lead to a quick end to the war.

The Roman legions forced their way through Hannibal's deliberately weak centre, but Libyan heavy infantry on the wings swung around their advance, menacing their flanks.

[109] Toni Ñaco del Hoyo describes the Trebia, Lake Trasimene and Cannae as the three "great military calamities" suffered by the Romans in the first three years of the war.

Livy gives a fuller record, but according to Goldsworthy "his reliability is often suspect", especially with regard to his descriptions of battles; many modern historians agree, but nevertheless his is the best surviving source for this part of the war.

[126] When the port city of Locri defected to Carthage in the summer of 215 BC it was immediately used to reinforce the Carthaginian forces in Italy with soldiers, supplies and war elephants.

Hiero II, the old tyrant of Syracuse of forty-five-years standing and a staunch Roman ally, died in 215 BC and his successor Hieronymus was discontented with his situation.

In 211 BC Hannibal sent a force of Numidian cavalry to Sicily, which was led by the skilled Liby-Phoenician officer Mottones, who inflicted heavy losses on the Roman army through hit-and-run attacks.

[141] For 11 years after Cannae the war surged around southern Italy as cities went over to the Carthaginians or were taken by subterfuge and the Romans recaptured them by siege or by suborning factions within to give them entry.

He next marched his army towards Rome, hoping to compel the Romans to abandon the siege to defend it; however, the besieging force stayed in place and Capua fell soon afterwards.

[159] The Roman fleet continued on from Massala in the autumn of 218 BC, landing the army it was transporting in north-east Iberia, where it won support among the local tribes.

Hasdrubal demurred, arguing that Carthaginian authority over the Iberian tribes was too fragile and the Roman forces in the area too strong for him to execute the planned movement.

In 215 Hasdrubal eventually acted, besieging a pro-Roman town and offering battle at Dertosa,[162][160] where he attempted to use his cavalry superiority to clear the flanks of the Roman army while enveloping their centre on both sides with his infantry.

[168] In a carefully planned assault in 209 BC he captured the lightly defended centre of Carthaginian power in Iberia, New Carthage,[168][169] seizing a vast booty of gold, silver and siege artillery.

[189] Rome's African ally, King Masinissa of Numidia, exploited the prohibition on Carthage waging war to repeatedly raid and seize Carthaginian territory with impunity.

The campaign ended in disaster at the battle of Oroscopa and anti-Carthaginian factions in Rome used the illicit military action as a pretext to prepare a punitive expedition.