In the wake of its defeat in the First Punic War (264–241 BC) Carthage expanded its territory in south-east Iberia (modern Spain and Portugal).

The Roman Senate ratified a draft treaty, but because of mistrust and a surge in confidence when Hannibal arrived from Italy, Carthage repudiated it.

[3] The war lasted for 23 years, from 264 to 241 BC, and was fought primarily on the Mediterranean island of Sicily, its surrounding waters and in North Africa.

[3] The Carthaginians were defeated[4][5] and by the terms of the Treaty of Lutatius evacuated Sicily and paid Rome an indemnity of 3,200 silver talents[note 1] over ten years.

[8] Four years later, Rome seized Sardinia and Corsica on a cynical pretence and imposed a further 1,200 talent indemnity,[note 2][9][10] actions which fuelled Carthaginian resentment.

[11][12] The near-contemporary Greek historian 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.

[16] In 219 BC Hannibal, the de facto ruler of Carthaginian Iberia, led an army to Saguntum and besieged, captured and sacked it.

[19] In 218 BC Hannibal led a large Carthaginian army from Iberia through Gaul, over the Alps and invaded mainland Italy.

[21] The historian Toni Ñaco del Hoyo describes these as "great military calamities",[20] Brian Carey writes that they brought Rome to the brink of collapse.

In 211 BC the Romans suffered a severe reverse at the battle of the Upper Baetis and were penned back by the Carthaginians to the north-east corner of Iberia.

[27] 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; they each carried several javelins, which would be thrown from a distance, a short sword and a 90-centimetre (3 ft) shield.

[31] It was the long-standing Roman procedure to elect two men each year as senior magistrates, known as consuls, who in time of war would each lead an army.

[50] He was denied the triumph he would normally have expected on the grounds that he had not occupied any of the magistracies of the cursus honorum, the sequential mixture of military and political administrative positions held by aspiring Roman politicians.

Hannibal was still on Italian soil; there was the possibility of further Carthaginian invasions,[54] shortly to be realised when Mago Barca landed in Liguria;[55] the practical difficulties of an amphibious invasion and its logistical follow up were considerable; and when the Romans had invaded North Africa in 256 BC during the First Punic War they had been driven out with heavy losses, which had re-energised the Carthaginians.

[56] Eventually a compromise was agreed: Scipio was given Sicily as his consular province,[57] which was the best location for the Romans to launch an invasion of the Carthaginian homeland from and then logistically support it, and permission to cross to Africa on his own judgement.

[54] But Roman commitment was less than wholehearted: Scipio was not allowed to conscript troops for his consular army, as was usual, but could only call for volunteers.

[29][35] With up to half of the complement of his legions being fresh volunteers, and with no fighting having taken place on Sicily for the past five years, Scipio instigated a rigorous training regime.

[60] Also during 205 BC 30 Roman ships under Scipio's second-in-command, the legate Gaius Laelius, raided North Africa around Hippo Regius, gathering large quantities of loot and many captives.

[64] The locals fled and Carthage's immediate response, a scouting party of 500 cavalry, was defeated with the loss of its commander and the general in overall charge of responding to the invasion.

Following a stratagem agreed with Scipio, Masinissa's cavalry raided Hanno's force who chased them off and then pursued them into a Roman ambush.

[80][83] With no Carthaginian field army to threaten them, the Romans pressed their siege of Utica and pillaged an extensive area of North Africa with strong and far-ranging raids.

[85] When he heard that the Carthaginians were reassembling their army, Scipio left a force to continue the siege of Utica and led the rest on a rapid march to the Great Plains.

The two legions of Latin allies charged the opponents facing them and again the Carthaginian and Numidian infantry put up little or no resistance before turning and fleeing.

[89] Many of the men of these units had been involved in the recent debacle of the burning camps at Utica and the memory of having been beaten by the same Roman army reduced their morale to the point that they had no stomach for the fight.

Once he saw that his hastati were holding their own Scipio did not follow normal practice, which would have been to feed in men from the second rank of principes to replace casualties and relieve tired fighters.

Instead he had the principes and triari of each legion form a column, march parallel to the line of battle and then round to attack the Iberians in the flank and rear.

[91] The historian Nigel Bagnall considers it a "foolish decision" by Hasdrubal to fight a battle with an army consisting entirely of men who were either demoralised or new recruits and whose state of training was "deplorably low".

[96] The Roman Senate ratified a draft treaty, but because of mistrust and a surge in confidence when Hannibal arrived from Italy, Carthage repudiated it.

[97] Hannibal was placed in command of another army, formed of his and Mago's veterans from Italy and newly raised troops from Africa, with 80 war elephants but few cavalry.