Battle of the Trebbia: Hannibal's Carthaginians Defeat Romans to Open the 2nd Punic War

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Battle of the Trebbia: Hannibal's Carthaginians Defeat Romans to Open the 2nd Punic War

Battle of the Trebbia, 218 BC (artist unknown)
Image courtesy of
(Unless otherwise indicated, all illustrations are courtesy of Wikipedia)

Today in Military History: December 18, 218 BC

For this week's stroll through military history, we'll journey back to the late 3rd century, BC. The Carthaginian general Hannibal Barca was bent on avenging his country's defeat in the First Punic War (264-241 BC). The Roman Republic believed its Italian homeland was safe from attack by the North African Carthaginians; Hannibal proved them wrong.


Carthage and Rome came into competition in the early 3rd century BC. Carthage's commercial network controlled the western Mediterranean Sea. The maritime nation – founded by Phoenician merchants in the 9th century on the seacoast of what is today Tunisia – possessed the largest navy in the area. Their land armies were mainly hired mercenaries or allies.

Meanwhile, Rome had gained control of the majority of the Italian peninsula below the Po River through use of its highly trained citizen army. At that time, Rome did not have a navy. However, as happened throughout Roman history, they were quick learners.

The two nations finally came to blows over the island of Sicily. The majority of the island was under Carthaginian control, but a local dispute between two towns on the island brought the two major powers into conflict. It was a protracted 25-year conflict, which saw Rome quickly build a creditable navy, and the men the city on the Tiber learned new tactics. Finally, in 241 Carthage signed a peace treaty under the terms of which they evacuated Sicily and paid Rome a large war indemnity. The long war was costly to both powers, but Carthage was more seriously affected.

The treaty ending the war was innately inequitable to the North African nation. Rome acquired the islands of Corsica and Sardinia, and gained effective control of Sicily. The pact also forced Carthage to pay a huge indemnity to Rome, which crippled the Carthaginian economy and prevented the recruiting of more mercenary soldiers, forcing them to rely more and more on allied troops.

Mediterranean in 218 BC; Roman territory in blue, Carthaginian in dark red; Image created by Wikipedia user Goran tek-en
Mediterranean in 218 BC; Roman territory in blue, Carthaginian in dark red
Image created by Wikipedia user Goran tek-en

This turn of events did not stop the Carthaginians, however. One of the nation's most renowned leaders, Hamilcar Barca, developed a new strategy to increase the nation-state's finances and threaten Rome. Barca expanded Carthaginian control of lands in Iberia (modern-day Spain) and opened a number of new silver mines. The silver became the basis of Carthage's economy, and allowed Barca to raise a large army in Iberia under his command. [Hamilcar Barca was basically functioning as an independent warlord, with the approval of – but no real oversight by – the Carthaginian government.] Hamilcar either died in battle with an unnamed Iberian tribe, or drowned while fleeing from the battle. Eventually he was succeeded by his eldest son Hannibal.

Consequently in 219, Hannibal (26 years of age at the time) led Carthaginian forces in a siege against the town of Saguntum, located deep in the area of Iberia under Punic control. This city was a large, heavily fortified commercial center which was independent but allied to Rome. The Saguntines sent frantic messages to Rome asking for military assistance; unfortunately for them, Roman legions were involved in putting down revolts in Illyria (modern-day areas of northern Albania, Bosnia and Herzegovina, Montenegro, and coastal Croatia). Rome never reacted until it was too late.

After an eight month siege, Saguntum fell to Hannibal's forces. After the inhabitants refused the terms of surrender, the Carthaginians put the population to the sword (though some sources say many of the Saguntines committed suicide rather than live under Hannibal's rule). Once word of the fate of Saguntum reached Rome, the Senate declared war on Carthage.

Hannibal's March on Rome

During his childhood, Hannibal had been brought up to despise Rome. He promised before the gods of Carthage that he would never be a friend of the Roman Republic. It was his father's teachings that propelled Hannibal to be one of the world's greatest military leaders.

Roman bust reputedly of Hannibal, discovered in Capua, Italy; Sculptor and date of creation unknown
Roman bust reputedly of Hannibal, discovered in Capua, Italy
Sculptor and date of creation unknown

In the late spring (probably May) of 218, Hannibal and his army left Iberia to march overland to Italy, with the eventual objective being the capture and destruction of Rome. His original army consisted of 90,000 heavy infantry – mostly from various African and Iberian nations – and 12,000 cavalry and about 100 elephants. Fighting his way north of the Ebro River and eventually through the Pyrenees Mountains – Hannibal assigned some 20,000 of his men to garrison duty in the newly-conquered area of Iberia. In addition, he sent home some 11,000 of his original recruits. By this time, Hannibal's invasion force was reduced to 50,000 infantry and 9000 horsemen.

After marching through southern Gaul (France), the first major obstacle to his army's journey was reached: the Rhône River. A confederation of Gallic tribes on the eastern side of the Rhône was determined to prevent Hannibal's forces from proceeding further (perhaps encouraged by Roman bribes). However, Gallic tribes allied to the Carthaginians on the western side of the river provided the invaders with boats, rafts, and canoes to ferry the army across the Rhône.

After fording the Rhône in late September, Hannibal's army – numbering 38,000 infantry, 8,000 cavalry, and about 80 elephants – continued its overland march, reaching the Alps sometime in October. With the exception of the crossing of the Rhône River, the Carthaginian expedition had been amazingly uneventful. Though the invaders had been met by a number of less-than-friendly tribes, Hannibal seemingly exerted a great deal of diplomacy to aid the continuing journey of his polyglot force.

Things changed as the Carthaginians began to traverse the Alps. Winter came early, with snow, ice and wind making the mountain passes treacherous. In addition, native Gallic tribes began to oppose the invaders, setting ambushes, causing rockfalls, and generally making life miserable for the mainly warm-weather Carthaginians and Numidians in Hannibal's army.

However, after an arduous march of just over two week, the invaders came down onto the northern plains of Italy, dominated by the Po River. His army had shrunk – through fighting, exposure to the elements, and desertions – to about 28,000 infantry, 6000 cavalry, and only about 40 elephants. Things did not look good for the Carthaginian commander, however…

Hannibal's army crossing the Alps, artist unknown; Image courtesy of
Hannibal's army crossing the Alps, artist unknown
Image courtesy of

Prelude to the Battle

Prior to setting out on his invasion, Hannibal had contacted a number of Gallic tribes living in the north of Italy (the Roman province of Cisalpine Gaul). To them he outlined his plan to eliminate Rome. Upon his arrival, he received supplies and food from the rebellious Gallic tribes. Hannibal also had little problem recruiting replacements for his casualties from these tribes.

Continuing the invasion, Roman leadership now realized that they were in grave danger. Roman forces were waiting in Cisalpine Gaul under consul Publius Cornelius Scipio. The consul had been assigned to invade Iberia and attack Hannibal's forces before they entered Gaul. Finding the Carthaginian army already on the march, Scipio sent part of his soldiers on to Iberia, and then he and the remainder of his forces sailed back to Italy to confront Hannibal.

At the battle of Ticinus, in November, the two forces were first engaged in a small confrontation. Light troops send by Scipio to scout the enemy were met by Numidian cavalry and soundly defeated. As only a prelude of things to come, the most significant results were Scipio receiving a serious wound during the battle and the opening of additional Gallic recruitment to Hannibal. The Romans were forced to withdraw to the town of Placentia to plan for another attack.

When word reached Rome of this minor engagement, a message was sent to consul Tiberius Sempronius Longus, who was recruiting new soldiers in Sicily. He was directed to return to Italy and head north to confront the Carthaginian invasion. Consul Sempronius and his army arrived at the Adriatic town of Ariminium (modern-day Rimini) sometime in early December, and promptly marched northwest toward Placentia to consolidate his army with Scipio's forces.

In mid-December, consul Sempronius met with his fellow consul Scipio, who was still recovering from his wound sustained at the Ticinus. While they discussed cooperation to blunt Hannibal's invasion, Scipio declined to take the field, recommending that his fellow consul's newest units would benefit from additional training. [Scipio's camp was several miles southwest of Placentia.] Sempronius, taking his own counsel, continued toward Placentia, and made camp about a mile west of that town on the east side of the River Trebbia. Hannibal's army was placed about a half-mile west of the Roman encampment, on the western side of the river.

Carthaginian Army

Thanks to his recruiting among the Gallic tribes of northern Italy and of the nearby Ligurians, the Carthaginian army had expanded to about 40,000 men – 21,000 heavy infantry, 8000 light infantry, 11,000 cavalry, and about 37 elephants. The heavy infantry contingent consisted of Ligurians, Libyans, Gauls, and Iberians, possibly with some native Carthaginians also in the mix. There may even have been some true mercenaries, possibly from Greece or Macedonia, or any number of former Greek colonies like Syracuse or Massalia (Marseilles). The light infantry was likely Gallic and Iberian javelinmen and Balearic slingers. The cavalry – both light and heavy – was composed mainly of Numidians and probably Gauls or Iberians.

Roman Army

There are two main histories that chronicle this battle: The Histories by Polybius, a Greek historian of the 2nd century BC; History of the City of Rome by Livy, who lived in the late 1st century BC into the early 1st century AD. Both men's writings address the battle of the Trebbia, but certain details are unknown or contradictory. One of these details is the size of the Roman army.

Modern historians speculated that the Roman army consisted of 42,000 men: 18,000 Romans, 20,000 Italian allied infantry, and 2000 cavalry (both Roman and allied). The Romans likely consisted of 4 legions (two possibly acquired from consul Scipio's forces) with 2000 additional men that were new recruits with no previous experience. The allied units were trained and organized in a fashion similar to the Roman legionaries. The Roman cavalry mainly consisted of native Romans with a smattering of allies.

Battle of the Trebbia

Early on the morning of December 18, Hannibal's Numidian cavalry launched a harassing raid on Sempronius's camp. The surprise attack provoked the impetuous Roman consul to begin the battle. He ordered his forces to rise from their beds and form up for action. [The Romans and their allies had not partaken of breakfast, which would come into play later.] It took the Roman army a few hours to fully organize, so that around noon, the Romans and their allies crossed the cold, swollen waters of the Trebbia to confront the enemy. Hungry and cold, the Roman army was already at a severe disadvantage.

Seeing the Carthaginian army already in line of battle, the Roman light infantry (the velites) began the attack, throwing their pila (javelins) at the enemy. The Roman and Punic light infantry fought to a standstill.

Sempronius ordered his men to attack the Carthaginian battle line, with the two cavalry wings opening the main battle. Unfortunately, they were outnumbered at least 2 to 1 by the Numidian and Gallic horsemen. In addition, the Punic elephants terrified the Roman cavalry. The unequal battle was brief, with the Roman horsemen retreating as fast as their steeds could go. The Carthaginian cavalry, rather than pursue their beaten foes, turned and attacked the flanks of the Italian infantry units.

Battle of Trebbia, 218 B.C., 2nd Punic War, between Carthaginians and Romans
Battle of Trebbia, 218 B.C., 2nd Punic War, between Carthaginians and Romans.
1 Carthaginian camp, 2 Carthaginian horse, 3 Carthaginian infantry, 4 Mago Barca's detachment,
5 Trebbia River, 6 Roman horse, 7 Roman infantry, 8 Roman camp, 9 Po River,
0 City of Placentia (modern-day Piacenza)

The combination of the Carthaginian, Iberian, and Gallic infantry added to the pressure exerted by the Punic horsemen began to wear on the Roman allies. Standard Roman military practice placed native Roman footmen in the center of the army's formation, with allied Italian units flanking them on both sides.

The Roman legionaries which formed the core of their infantry line were having good success against the Iberian and Gallic soldiers. At this point in the combat, the Roman center was very near to breaking through the Carthaginian center. However, Hannibal made the decision to play his ace-in-the-hole…

During his battle preparations the previous evening, Hannibal selected an elite force of 2000 men – half infantry, half horsemen – to hide nearby behind a marshy, forested stream to lay in wait for the battle's climax. He placed his son Mago Barca in command of these troops. After several hours of vicious hand-to-hand combat, Hannibal gave the signal for his ambush force to come into action.

The hidden Carthaginian ambushers struck the rear of the weakening Roman infantry. With pressure from front, flank, and now rear, the first portion of the Roman infantry formations to crack were the Italian allied units. The Roman center – now consisting of about 10,000 tired, famished veterans – formed a square to give them an all-around defense. By late afternoon, consul Sempronius realized his army was scattered and defeated. He gave the order for his infantry square to break contact with the Punic army and, in good order, the surviving Romans marched to the town of Placentia to safety. The Carthaginians did not pursue. The battle of the Trebbia was over…


As with most battles from ancient times, exact casualty counts are unavailable. It is estimated that the Roman army suffered between 28,000 and 32,000 dead and wounded. Why no one missing, you may ask? Well, Hannibal made his policy that any enemy fighters captured after a battle would be asked the key question, "Are you a native Roman?" If the reply was positive, the individual would be killed out of hand. Any Italian allied soldiers would be let go. This allowed Hannibal to demonstrate to the Roman allies that his fight was with Rome. It was also hoped that mercy to non-Romans would give the Carthaginians a leg up on recruiting allies of their own against the Romans.

Carthaginian casualties were probably fairly light, perhaps 3000-5000 killed and wounded. The only major loss for Hannibal was his elephant corps, of which it is reported only one survived the fight at the Trebbia.

Footnote #1: Over the next 16 years, Hannibal and his invading forces ranged up and down the Italian peninsula. They gained allies, lost allies, and consistently defeated most Roman armies sent against them. However, because he lacked any siege engines, Hannibal never achieved his objective of destroying Rome. It wasn't until 203 BC that a Roman invasion of the Carthaginian homeland forced him to abandon his Italian campaign and return to Africa.

Footnote #2: The actual site of the battle of the Trebbia is still unknown. Both the rivers Po and Trebbia have change their courses over the past 2200 years.

Footnote #3: As a result of the poor performance of the Roman cavalry at the Trebbia, Roman-born noble equestrian horsemen were never again recruited for service. From then on, Roman cavalry consisted of allies or hired mercenaries, mainly Gallic or German horsemen.

Footnote #4: There is speculation that Sempronius, besides his natural impetuosity, was hoping to ride a battlefield victory to a victory at the ballot box. The annual elections for consul were scheduled for January. He returned to Rome the next month to oversee the elections (he was not re-elected, but did return to the command of his army.)

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