Only one draft of reinforcements ever reached Hannibal by sea, when Bomilcar landed at Locri in 215. A combination of Hannibal's lack of a major port, the Carthaginians' failure to drive the Romans from Sicily and win naval dominance of the sea routes around the island, and apathy amongst the leadership at Carthage, prevented a repeat of this convoy. It seems clear that from the beginning Hannibal hoped to be reinforced by an army from Spain following the overland route he had taken himself. Hasdrubal Barca is said to have been planning such an expedition in 216 when it was rendered impractical by Roman successes in Spain. The need to restore Punic fortunes in Spain also led to the redirection of the troops raised in Europe by Mago Barca which had originally been intended to go to Italy. Hasdrubal tried again in 208 and successfully led an army out of Spain despite being defeated in a rearguard action at Baecula. He seems to have followed a similar route to his brother but does not appear to have had to fight the local tribes as often, with the result that his smaller army suffered fewer casualties. Perhaps it helped that he was spending gold lavishly to hire mercenaries from amongst the Gallic tribes. Massilia sent messages to warn the Romans of his progress. Roman ambassadors were sent and through links of guest friendship between Massiliotes and some Gallic chieftains discovered that Hasdrubal expected to cross the Alps into Italy early in the spring of 207.29
The news caused panic at Rome. For a decade they had waged war against an enemy army on their own lands. Vast numbers of soldiers had been enrolled and kept permanently in service. Casualties had been huge and the financial cost to the state enormous, whilst wide swathes of the Italian countryside had been foraged over and devastated by the rival armies. After all the effort Hannibal remained undefeated and although he had been hemmed into a corner of southern Italy he was still capable of outwitting their commanders. The declaration of the twelve colonies in 209 might suggest that the State was nearing the end of its resources. Now another of Hamilcar Barca's sons was set to invade Italy with fire and sword. What if the two brothers were to join forces? Were there to be new 'Trebia's and 'Cannae's, and if so, could Rome survive?
One of the new consuls, Marcus Livius Salinator, who had only a few years before returned to political life following a self-imposed retirement after the scandals of his first consulship in 219, was sent north with an army. He was supported by one of the praetors, Lucius Porcius Licinus, who had two understrength legions based near Ariminum, whilst Varro led a similarly sized force on the other side of the Apennines in Etruria. Just like his brother in 217, Hasdrubal would be forced to choose which side of these mountains to advance down, so once again the Senate deployed armies to guard against both options. The Carthaginians descended from the Alps earlier than the Romans had expected, although Licinus heard of his advance and sent a message warning Rome and urging the consuls to join their armies as soon as possible. Once in the Po valley, Hasdrubal marched on Placentia and began to besiege the colony. Perhaps he wanted to rest his men after their march, or as Livy suggests wanted the prestige of an early victory, which might certainly encourage the Gallic tribes to muster to him. However, the town's defenders proved more resilient than he had anticipated and he abandoned the blockade. Six riders, two Numidians and four Gauls, were sent with sealed letters to find Hannibal. As usual in the campaigning season, Hannibal's army was constantly on the move and it was near Tarentum that some of the messengers were arrested by a Roman patrol. After interrogation their letters were discovered and sent to the Senate, who read in them that Hasdrubal hoped to meet his brother in Umbria. Livy provides no detail as to precisely where in this large area the rendezvous was supposed to occur. Clearly it was somewhere on the east coast, perhaps near the southern edge of the ager Gallicus. Hannibal remained in the south as his brother began to push down the east coast of Italy.
This was not like 218. The Romans were in a far higher state of mobilization, their leaders and armies more experienced and effective. Their response to the news of the Carthaginians' intentions was rapid. Somewhere, perhaps near Sena Gallica, Hasdrubal was confronted by the combined armies of Salinator and the praetor Licinus, who had retreated ahead of the enemy, delaying their march as much as possible. The other consul, Caius Claudius Nero, had a somewhat ambiguous reputation for boldness verging on rashness. At the beginning of the year he had been sent to lead the armies containing Hannibal in the south and was near Canusium when he received the intercepted message. Nero decided to take the pick of his army, some 6,000 foot and 1,000 cavalry, and lead them north to join his colleague. Instructions were sent out to the communities along his planned route ordering them to prepare food and supplies for his soldiers who were to march unburdened. The towns were also to make ready carts and mules to give lifts to the weary men in the column. Then, spreading a rumour that he intended a surprise attack on a nearby city, Nero marched out of camp at night and after a short distance swung north towards Picenum. As they marched crowds cheered them on their way, furnishing the requested supplies. The reaction in Rome to the report of the consul's move was less certain, as many feared that the remainder of the army he had left in Apulia might be vulnerable to Hannibal's attack. Livy does not say how long this forced march of around 250 miles took Nero's men, although he does claim that the return journey was completed even more quickly, in only six days. Clearly it was fast enough to surprise Hasdrubal, and the Romans took care to conceal this reinforcement. Messengers were sent ahead to Salinator and it was arranged for the column to march in under cover of darkness and that the men were then to be led as quietly as possible by the individual soldiers in the camp to the tents they would share. Although Hasdrubal's camp was a mere 500 paces - half a Roman mile - away, the deception worked.31
The next morning Nero persuaded his colleague and the praetor to risk a battle immediately, preferring the benefit of surprise over allowing his footsore soldiers to rest. Hasdrubal had already formed his army in battle order outside his camp as the Romans marched out to deploy. However, he is said to have noticed amongst the Roman line men with old shields he had not seen before, and cavalry with lean horses, as well as having a general impression of an increase in Roman numbers. Worried, Hasdrubal refused battle and the Romans, as was usual, did not force an engagement with an enemy who refused to advance far from his camp. Patrols were sent out to observe the separate camps pitched by Licinus and Salinator. Livy tells us that they reported two trumpet fanfares in the consul's camp and only one in the praetor's camp, which Hasdrubal correctly understood as meaning that a second consul must also be present. The size of Hasdrubal's army is unclear, but it seems probable that the addition of the equivalent of a strong legion to the Roman armies facing him convinced him that a battle was unwise. In the night he retreated towards the River Metaurus. Livy claims that his guides, presumably local men, deserted and that the Punic column went astray in the darkness, but night marches have always been difficult and it is possible that the mistake was accidental. Later in the night Hasdrubal reached the river bank and ordered his units to follow it, hoping to strike the proper road by the light of dawn and so discover a crossing place.
The Romans began the pursuit as soon as they realized that the enemy had retreated. Nero led with the combined cavalry of the three armies, followed by Licinus with the velites and Salinator, under whose auspices the battle was fought, with the main army. They caught up with Hasdrubal when the latter had decided that his men needed rest and so had begun to construct a camp on a hill overlooking the river. As the various elements of the Roman armies arrived and began to form a battle line, the Carthaginian ordered his men to stop work on the camp and deploy. Both sides must have been tired after their march, but the Roman commanders were eager for battle and did not intend to delay. The precise location of the battle of Metaurus is unknown and the suggestions have varied widely. The terrain seems to have been fairly uneven and the open space limited, and this, combined with the haste with which each side formed up, made the battle less regular than Hannibal's early campaigns and more like the fighting in southern Italy. Nero commanded the Roman right wing, apparently with his own infantry and cavalry; Licinus held the centre and Salinator the left. It is unclear whether all the cavalry were divided between the extreme left and right wings as was the usual practice, although Livy seems to imply that the bulk of the Roman cavalry were with Salinator on the left which may mean that Nero had the allied horse. Hasdrubal stationed his ten elephants (fifteen according to Appian32) ahead of his centre, and placed his best troops, the Spanish, on the right and the Gauls on the left. According to Livy his centre behind the elephants was composed of Ligurians, but Polybius does not mention their presence at all in his account, although he may simply have lumped them in with the Spanish. Neither Livy nor Polybius make any specific mention of Carthaginian cavalry. The Gauls were on high ground in a very formidable position, certainly impossible to take by a frontal attack and perhaps difficult even to reach. The Punic centre and left were deployed unusually deep, probably a reflection of the confined space and the haste with which they had formed up. The Romans are unlikely to have had many more than 40,000 men and Hasdrubal significantly fewer, but these numbers must remain conjectural.
The battle began when Hasdrubal launched his main assault against Salinator and the Roman left, who advanced to meet him. Livy claims that the elephants disordered the hastati and created a temporary advantage, but then panicked and spread confusion on both sides. The fighting was fierce and no clear advantage was achieved by either side as both Salinator and Hasdrubal were closely involved in the fighting, directing and encouraging their men by personal example. On the right, the Romans could make no headway against the position held by the Gauls and were unable to find a way of outflanking it. Nero then made a remarkably bold and imaginative decision on his own initiative. Taking many of the men from his wing, he led them in a march behind the Roman battle line and around the enemy's extreme right flank. They then attacked the Spanish in the flank, turning the tide decisively in the Romans' favour. The Punic right and centre collapsed into rout under this unexpected onslaught. Hasdrubal, realizing that the day was lost, died fighting heroically or, according to another tradition, committed suicide. The Romans rolled up the entire army, driving the Gauls from their hilltop and storming the Punic camp. More Gauls are said to have been discovered there, most lying in a drunken stupor in their tents. It is possible that Hasdrubal's recently recruited Gallic allies had as poor march discipline as the tribesmen Hannibal had had to drive along in 217. For troops unused to campaigning, the long and confusing night march would have proved very fatiguing.
Polybius tells us that 10,000 of Hasdrubal's men fell in the battle for the loss of 2,000 Romans, far more plausible figures than the huge totals given by Livy. Six elephants were killed and the other four rounded up in the aftermath. It was a great Roman victory and the entire campaign demonstrated the higher efficiency and greater flexibility of Roman armies compared to the beginning of the war. The Romans had responded quickly to news of the enemy's intentions, arranging to intercept Hasdrubal with two armies, which were then reinforced by a strong detachment from a third. Nero's march was a triumph not just for discipline and determination, but for the logistical organization which allowed him to arrange in a matter of days for supplies to be prepared in advance along his route. His decision to march from one wing to outflank the enemy on the opposite end of the battlefield displayed a degree of tactical flexibility unimaginable in the legions of 218. The same level of skill was also to be shown by Scipio Africanus' armies in Spain and Africa.33
The relief at Rome was overwhelming when news of this victory was received, and three days' public thanksgiving was declared by the Senate. Even more so, according to Livy, when it was learned that Nero had rejoined his own army in Apulia before Hannibal had been able to take advantage of his absence. The last great crisis of the war in Italy had been averted. Livius Salinator was awarded a triumph for his victory, and Nero, who had been his subordinate, the lesser honour of an ovation. However, Livy claims that when Nero rode on horseback behind Salinator's chariot the cheers were louder for him, the crowd believing that he had been the real architect of the victory. By archaic tradition Roman soldiers who marched in a triumph sang ribald verses at their commander's expense. Nero received the slightly dubious honour of being the target of more of these jibes than his senior colleague.34