Famous Roman Battles: 12 Decisive Engagements

For more than a thousand years, Roman armies fought — and usually won — on battlefields from Scotland to Mesopotamia. The history of those battles is the history of the empire itself: the consolidation of Italy, the destruction of Carthage, the conquest of Gaul, the eclipse of the Republic, the expansion into Britain and Dacia, the long defense of the frontiers, and finally the disintegration of the western provinces. This article covers twelve of the most decisive of those engagements, in chronological order, with the background, commanders, tactics, and consequences of each.

For a broader look at the Roman military, see The Roman Legion. For the formations used in these battles, see Roman Military Tactics and Formations.

1. The Battle of the Lake Regillus, 499 BCE

The earliest battle in the long line of Roman military history was fought, according to tradition, beside a volcanic lake in Latium, a few miles east of Rome. The Battle of Lake Regillus was the decisive engagement of the second war between Rome and the Latin League, in which the two sides fought for control of central Italy. The Roman army was led, according to Livy, by the dictator Aulus Postumius, while the Latin coalition was commanded by the exiled Roman general Octavius Mamilius.

The Romans used a fresh tactical innovation. They stationed 1,000 men in reserve behind a hill, hidden from the Latin view, and committed them at the moment when the Latin line had been fully engaged. The reserve charged downhill into the Latin flank and turned the battle. According to the Roman historian, the legendary twins Castor and Pollux were seen fighting on the Roman side, and a temple was dedicated to them in the Forum in gratitude.

The battle did not end the war, but it did break the back of the Latin coalition. Within decades Rome had concluded a series of treaties that brought the Latin cities into its expanding sphere of influence. The detail of the reserves used at Regillus is hard to verify, but the broader tradition of the Latin Wars established the framework for Rome’s conquest of the Italian peninsula.

2. The Battle of Cannae, 216 BCE

The single greatest disaster in Roman military history, and one of the most studied tactical defeats in world history, was the Battle of Cannae. In the summer of 216 BCE, on a flat plain near the Aufidus River in Apulia, Hannibal of Carthage destroyed eight Roman legions — perhaps 70,000 men — in a single afternoon.

Hannibal’s plan was a double envelopment. He deployed his African heavy infantry in the center, his Spanish and Celtic infantry on the wings, and his Numidian cavalry on the wings beyond. As the Roman legions, drawn up in their manipular triple line, charged forward, the Carthaginian center deliberately yielded. The Romans pushed in, but the more numerous cavalry on the wings crushed the Roman cavalry and wheeled inward, behind the Roman line. When Hannibal ordered his center to resume the advance and his wings to close in, the Roman army was surrounded on three sides. The slaughter lasted hours.

Cannae became the textbook example of the encirclement and double envelopment. The German general Schlieffen would plan the opening of the First World War around the same maneuver, only to fail where Hannibal had succeeded. The disaster forced the Romans to adopt much more cautious tactics under the general Quintus Fabius Maximus, surnamed “Cunctator” — the Delayer — and ultimately led to the reform of the legion into the cohortal system.

3. The Battle of Zama, 202 BCE

Sixteen years after Cannae, the Romans met Hannibal again, this time on African soil. The Battle of Zama, fought near modern Tunis, was the decisive engagement of the Second Punic War and one of the most innovative tactical performances of the ancient world. The Roman army was commanded by Scipio Africanus, the 32-year-old general who had already driven the Carthaginians from Spain.

Scipio deployed his legions in a checkerboard formation of maniples, with deliberate gaps between the units. Hannibal opened with a charge of 80 war elephants; Scipio ordered the cohorts to sound their trumpets and let the elephants pass through the gaps, where they were killed by javelins from the supporting units. The Roman and Carthaginian infantry then engaged in a long, even contest, while Scipio’s cavalry — held back at the start of the battle — rode around the back of the field and crashed into the rear of the Carthaginian line. Hannibal’s army broke and was slaughtered as it fled.

Zama ended the Second Punic War and made Rome the master of the western Mediterranean. The battle is also the textbook example of the combined use of infantry and cavalry reserves, and Scipio Africanus became the model for every Roman general who followed.

4. The Battle of Alesia, 52 BCE

In the heart of Gaul, in the autumn of 52 BCE, Julius Caesar completed the conquest of the Gallic tribes by besieging the war leader Vercingetorix and his army inside the hill fort of Alesia. What made Alesia unique in the history of siege warfare was that the besiegers were themselves besieged. Vercingetorix had sent messengers out before the siege closed, and a great relief army of perhaps 250,000 Gauls had gathered on the plateau to his north.

Caesar built two walls. The circumvallation faced in, sealing Vercingetorix inside Alesia. The contravallation faced out, holding off the relief force. The two walls, 25 kilometers of elaborate earthworks studded with forts, towers, and traps, were completed in a few weeks by Caesar’s 50,000 men working around the clock. When the relief army attacked in concert with a sortie from inside, Caesar moved his army between the walls, throwing the XII Legion into the outer defenses and fighting the sortie with the rest.

The relief army broke off the siege, and Vercingetorix surrendered. The fall of Alesia ended the great Gallic revolt and effectively completed the Roman conquest of Gaul. It also established Caesar as the most formidable general in the Roman world, a reputation he would shortly turn against his own state.

5. The Battle of Actium, 31 BCE

The Battle of Actium was the naval engagement that decided the Roman civil war between Octavian, the adopted son of Julius Caesar, and Mark Antony, the general who had allied himself with Cleopatra of Egypt. Fought off the western coast of Greece on 2 September 31 BCE, the battle was decided as much by psychology as by tactics.

The two fleets were roughly equal: about 400 warships on each side. Octavian’s admiral, Marcus Vipsanius Agrippa, used smaller, more maneuverable liburnae to harass Antony’s heavier ships. Antony drew his fleet out of the Bay of Actium in a long line, hoping to use the wind and his bigger ships to overwhelm Octavian. Cleopatra, with 60 Egyptian ships, was in the rear. The fleets engaged, and Antony held his own for several hours. Then Cleopatra’s squadron, for reasons still debated, broke through the line and made for the open sea. Antony followed with a small escort.

Agrippa, free of his main opponent, closed on Antony’s flagship and burned or captured most of his fleet. The survivors fled to Alexandria, where Antony and Cleopatra would commit suicide the following year. Actium ended the civil war, and Octavian — soon to be styled Augustus — became the first Roman emperor. The Republic was over.

6. The Battle of the Teutoburg Forest, 9 CE

For Rome, the Battle of the Teutoburg Forest was the most traumatic defeat in centuries. In September of 9 CE, an alliance of Germanic tribes under Arminius, a Cheruscan chief who had served as an officer in the Roman auxiliary cavalry, ambushed and destroyed three Roman legions — the XVII, XVIII, and XIX — as they marched through a forested, marshy stretch of western Germany.

Arminius had lured the Roman commander, Publius Quinctilius Varus, into the trap by reporting a fictitious tribal uprising. The Roman column, with its accompanying camp followers, was strung out over 15 to 20 kilometers of muddy track. The Germans attacked in a three-day running battle in driving rain, breaking the column into isolated pockets. The Roman soldiers, in heavy armor, were unable to deploy in the forest and undergrowth. The aquilae of all three legions were lost.

When the news reached Rome, the emperor Augustus was reportedly so shaken that he spent months wandering his palace crying, “Quintili Vare, legiones redde!” — “Quinctilius Varus, give me back my legions!” The defeat ended Roman plans to conquer Germania east of the Rhine, and the river remained the boundary of the empire for the next four hundred years. The battle is also the origin of the modern German national myth, dramatized in the HBO series Barbarians.

7. The Battle of Chalons, 451 CE

A century after the Teutoburg disaster, Rome faced an even graver threat: the Huns under Attila. In 451, Attila invaded Gaul with a huge army, and a Roman-Visigothic coalition under the general Flavius Aetius, sometimes called the “last of the Romans,” met him on the Catalaunian Plains near modern Châlons-en-Champagne. The day-long battle was confused, but the Romans and Visigoths held the field. Attila withdrew and invaded Italy the next year, failing to take Rome. He died in 453, and the Hunnic empire dissolved within a decade.

8. The Battle of Adrianople, 378 CE

For the second time in five centuries, the Roman Empire suffered a defeat on the plains of Thrace that shattered the imperial military. The Battle of Adrianople, fought on 9 August 378 CE, marked the death of the eastern emperor Valens and the destruction of the eastern Roman field army, and is often cited as the beginning of the end for the Western Roman Empire.

The enemy was the Goths, Germanic and Sarmatian peoples who had crossed the Danube into the empire as refugees and then as conquerors. The Roman general Frigeridus had been unable to contain them, and Valens himself marched east to take command. Against the advice of his nephew, the western emperor Gratian, who was bringing reinforcements from the west, Valens engaged the Gothic army on the afternoon of 9 August.

The Roman infantry, exhausted by a long march in summer heat, was drawn up in close order with the cavalry on the wings. The Gothic cavalry, mostly mounted archers, charged and then feigned retreat, drawing the Roman cavalry into a disordered pursuit. The Gothic infantry, including many armored wagons of laagered warriors, then closed in on the Roman foot. The Roman center was annihilated, and Valens was killed — whether on the field or in a farmhouse that was burned over his head is debated.

Adrianople was the first battle in centuries in which a Roman emperor personally commanded and died. It demonstrated that the traditional Roman reliance on heavy infantry could be defeated by combined-arms cavalry-and-foot action on open ground, and it presaged the rise of the heavy cavalry knight that would dominate medieval warfare.

9. The Battle of Philippi, 42 BCE

Less than a decade after Actium, another decisive battle of the Roman civil wars was fought in the hills of Thrace. The Battle of Philippi was a double engagement fought on 3 and 23 October 42 BCE, in which the forces of the Second Triumvirate — Octavian, Mark Antony, and Lepidus — defeated the republican legions of Brutus and Cassius, the assassins of Julius Caesar.

The first day saw a confused, costly battle in which the republican right under Cassius defeated Octavian’s left and the Triumviral right under Antony defeated Brutus. Cassius, mistakenly believing that Brutus had been defeated, committed suicide. The second battle, three weeks later, was the decisive one: Brutus’s army was overwhelmed, and Brutus killed himself. The republican cause died with him, and the second stage of the civil war was effectively over. Philippi established the dominance of the Triumvirate and paved the way for the final conflict between Octavian and Antony at Actium.

10. The Battle of Mons Graupius, 83 or 84 CE

In the far north of Roman Britain, Gnaeus Julius Agricola — father-in-law of the historian Tacitus — met the Caledonians in a battle vividly described by Tacitus. The Battle of Mons Graupius was fought somewhere in the Scottish Highlands and ended in a decisive Roman victory, with as many as 30,000 Caledonians killed for the loss of about 360 Romans.

Agricola’s 30,000 men drew up with auxiliary infantry in front and the legions behind, with cavalry on the wings. The Caledonians, led by Calgacus, charged downhill and broke through the auxiliary line, but the legions held and counterattacked. Caledonian war chariots and massed infantry could not break the Roman line, and the enemy was driven from the field.

Mons Graupius was the high-water mark of Roman expansion in Britain. Agricola was recalled by the emperor Domitian, and the Scottish frontier was abandoned. The Roman position in the north was later consolidated at the Antonine Wall and finally Hadrian’s Wall.

11. The Battle of the Milvian Bridge, 312 CE

The Battle of the Milvian Bridge was the engagement that decided the Roman civil war between the western emperor Constantine and the eastern emperor Maxentius, and it ushered in the Christianization of the Roman world. Fought on 28 October 312 CE on the Tiber north of Rome, the battle was decided by a tactical blunder.

Constantine, marching south from Gaul with about 40,000 men, faced Maxentius’s army of perhaps 75,000. According to Lactantius, Constantine had a vision the night before the battle — a cross of light in the sky with the words in hoc signo vinces (“in this sign, you shall conquer”) — and ordered his troops to paint the chi-rho monogram of Christ on their shields.

Maxentius had prepared a trap: a pontoon bridge connected to a boat-bridge that could be unmoored to dump troops into the river. The plan backfired when the Constantinian army pushed Maxentius’s troops back across the bridge, which collapsed under their weight. Maxentius drowned in the Tiber, weighted down by his armor. The battle made Constantine the Great sole emperor of the West. Within a few years the Edict of Milan made Christianity a legal religion, and it would soon become the official faith of the empire.