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For five centuries the Roman and Celtic armies and cultures clashed, pitting the most highly organized state of the ancient world against fierce individualists.

War horns brayed eerily, swords thudded against shields with a dull menace, and a jeering, terrifying howl went up from the roughly 12,000 Celtic warriors arrayed along the Allia River less than a dozen miles north of Rome. Their oblong shields were painted in reds, greens and other bright colors and decorated with boars, dragons and various designs. Facing them were approximately 24,000 Roman troops, the sun glinting off their bronze helmets and spear tips as they locked shields and braced for an attack. A lone Celt stepped from the line, sword held high. He yelled for a Roman champion to duel with him and sneered when none accepted. He then let out a piercing war cry, and the Celts surged forward, hurling their javelins before crashing into the Roman line. It was July 18, 390 BC, and the Celts and Romans were rushing headlong into a confrontation that would span several centuries.

The seasoned Roman army, most likely in a tightly packed phalanx formation, was unprepared for the might and fury of the Celtic charge. Physically bigger than the Romans, the Celts wielded long double-edged iron swords for slashing and sheltered behind body-length shields fitted with pointed metal bosses, which they punched into the enemy. Many wore chain mail. Led by the warrior chieftain Brennus, the Celts hacked through their opponents, driving them toward the river, decimating the Roman center and sending the survivors fleeing for Rome. Within days the victorious Celts entered, burned and pillaged the capital. The Celtic army occupied Rome for seven months until paid 1,000 pounds in gold to leave. According to legend, when a Roman tribune complained that the Celts’ scales were rigged, Brennus threw his sword and belt atop the counterweights, thus increasing the Roman ransom, and thundered, “Vae victis!” (“Woe to the vanquished!”). Brennus’ taunt, wrote the classical historian Livy, was “intolerable to Roman ears,” and thereafter the Romans harbored a bitter hatred of the Celts, whom they called Gauls. The Romans ultimately enclosed their capital within a massive wall to protect it from future “barbarian” raids.

The dramatic encounter along the Allia was among the first between two great European peoples who over the next five centuries or so would clash and interact in a complex intercultural weave of warfare, alliances and trade. Their interaction marked a collision of differing political systems—that of free-ranging tribes versus a highly regimented state bent on territorial and economic aggrandizement—and proved a mighty contest between the Celtic and Mediterranean ways of life. Ultimately, both civilizations would contribute significantly to the formation of the modern European identity.


The Celtic people comprised hundreds of tribes, some as small as 20,000 members and others boasting more than a quarter-million men, women and children. There wasn’t a uniform Celtic nation or state; what linked them was their Indo-European language, ethnicity and certain shared cultural characteristics and artistic styles. The Greeks called these diverse people the Keltoi, which is perhaps how the Celts referred to themselves. Probably due to population pressures and a desire for independence, the Celts were great migrators; the areas they inhabited stretched from Ireland and Scotland into Spain and France and farther east into parts of Germany, northern Italy, Greece, Eastern Europe and Turkey.

Celtic social structure radiated outward from the family to the extended family, clan, tribe and tribal alliances. “In Gaul,” Julius Caesar wrote in his Commentaries on the Gallic War, “there are factions, not only in every state and every village and district but practically in each individual household as well.” The Celts were talented farmers, skilled craftsmen and superb artisans, especially in metalwork and gold. Although Roman chroniclers often characterized them as brutish and primitive, the Celts constructed towns, roads and powerful hill forts. They mined salt and controlled the lucrative trade that resulted. They were masters at ironwork when the Romans were still using bronze. Celtic women enjoyed broad rights and status, some becoming military commanders, others queens. The Celts did not own slaves in any great numbers but readily sold captured enemies to the slaveholding Romans.

The Celts’ greatest shortcoming was that they left virtually no written records. Thus we are forced to rely on accounts from such Roman writers as Strabo, Caesar, Polybius and others who were predictably biased and oftentimes misinterpreted Celtic ways. Thanks to these Roman chroniclers, though, we have a somewhat accurate contemporary picture of the Celts.

Caesar, who fought the Celts for eight years in Gaul, noted there were “two types of men of distinction…the first is made up of the druids, and the other of the knights.” The druids were the intellectual and spiritual elite of Celtic society and served an apprenticeship of up to 20 years, becoming experts in philosophy and history and passing down knowledge and wisdom through oral traditions. Intimately in tune with the rhythms of nature, the druids held their ceremonies in oak groves. “Young men flock to them in large numbers to gain instruction,” Caesar wrote, “and they hold the druids in great esteem. For they decide almost all disputes, both public and private.” The druids also presided over animal and human sacrifices.

By “knights” Caesar was referring to the fighting class in what was an honor-based warrior society. “The whole race,” Strabo noted, “is madly fond of war, high-spirited and quick to battle but otherwise straightforward and not of evil character.” They excelled in raiding other tribes for revenge and rustling horses and cattle. Warfare was low intensity and conducted more for ritualized displays of individual prowess, skill and courage than to destroy or subjugate an enemy. Indeed, a specialized warrior society, the Gaesatae, fought naked except for arms and a shield. These elite troops had, Polybius wrote, “proud confidence in themselves” and seemingly fought in a state of divine power and purity. Sometimes warring tribes would square off only for the contest to be decided by two opposing champions who fought to the death, with the losing side retreating from the field. Celts were fond of boasting about their deeds and, according to Strabo, had a “love of decoration. They wear ornaments of gold, torques on their necks and bracelets on their arms and wrists, while people of high rank wear dyed garments besprinkled with gold.” After battle they held a grand feast of roasted boar with much drinking of beer and wine while highly respected bards sang of heroic deeds.


The Celtic warrior was armed with a long, straight sword, a large shield, two spears— one for thrusting, one for throwing—and a dagger. Some used slings, clubs and bows. The wealthy rode on horseback and cloaked themselves in chain mail of their own invention. In Britain they fought from two-horse chariots. They wore well-crafted and practical bronze or iron helmets, often fitted with a neck guard, and they usually dressed in colorful clothing fastened by intricate brooches of gold or silver. In Britain they painted their bodies with woad, a flowering plant that yields a dark blue dye.

The Celts were fierce, clever and brave in combat. During the 225 BC Battle of Telamon, Polybius’ history records, the Gaesatae occupied the leading rank, while other Celts formed according to family, tribe and clan. “[The Romans] were terrified by the fine order of the Celtic host and the dreadful din, for there were numerous trumpeters and horn blowers, and the whole army was shouting its war cries at the same time.…No less terrifying were the appearance and gestures of the naked warriors in front, all of whom were finely built men in the prime of life, and all in the leading companies richly adorned with gold torques and armlets.” The Celts placed chariots and war wagons on the flanks, while infantrymen gathered around their standards of sacred animals and deities.

Drawn up in a colorful line, the Celts would noisily approach the enemy, convinced of their superiority, bolstered by belief in an afterlife, eager to display their courage, and pleased to be fighting alongside family members and clansmen. Greek historian Diodorus Siculus recorded that often a lone warrior would “advance before the battle line to challenge the bravest of their opponents to single combat.”After this opening bout the Celts closed on their foe, throwing javelins and other missiles while parrying those hurled at them with their shields and swords. Finally, they rushed the enemy, using swords to shear faces and limbs, spears to thrust and shields to repulse opponents. This first fierce onslaught was intended to break a foe’s line and instill panic in his ranks.

In the wake of battle the Celts often beheaded enemy corpses and displayed their grisly trophies, for they believed the captured soul resided in the head. After looting the enemy dead, collecting their own wounded and burying their fallen, the Celts would throw their feast of roasted meat, wine and beer and boast of their martial prowess. The warriors would then return home or perhaps sack the enemy’s town. There was little thought of occupying land or establishing formal borders.

Conversely, city building was something at which the Romans excelled. By the time of the Battle of the Allia, Rome had grown from an insignificant village on the Tiber River into a regional power, its citizens having defeating the Etruscans and other Latin peoples in a long series of wars. In stark contrast to Celtic hill forts and villages, Rome was a magnificent metropolis of marble temples, paved avenues and arcaded marketplaces. An elected senate and two councils ruled, and it had a vigorous entrepreneurial class and a high standard of living. Thousands of slaves served Roman needs; yet Roman women lived more housebound and constricted lives than their Celtic counterparts. The Romans were proud of their achievements and gazed outward, seeking riches and glory beyond their borders. Thus the Celtic sack of Rome deeply shocked the young republic, leaving a lasting scar on the national psyche. Forever after July 18 was a day of ill omen.

The Romans had a professional army, manned by citizens who served up to 16 years and were rewarded with land and honors upon retirement. It was highly structured, with an officer corps, engineers, medics, auxiliaries, artillery and other specialized troops. The army’s basic unit was the legion, which in the early republic comprised some 3,000 men, increasing to about 4,200 in the imperial era. During the reign of Emperor Augustus (27 BC–AD 14) the army boasted 30 legions and roughly 165,000 men. Additionally, the Romans had an estimated pool of 6 to 7 million men from which to fill their ranks.

The army was among the most powerful and influential sectors of the Roman state. Ambitious men seeking political office and wealth were eager to serve in order to conquer foreign lands and capture booty—which they shared among their men to ensure loyalty—and to amass their own fortunes and prestige. But while generals held tactical command, the politicians in the capital kept them in check.

The Roman army was well trained and in a constant state of reform. After their humiliating encounter with Brennus, the Romans adopted Celtic chain mail, fashioned body-length rectangular shields, modeled their helmets after Celtic designs and, researchers have argued, abandoned the rigid phalanx in favor of the more flexible manipular legion, in which troops subdivided into blocks, or “centuries,” of men arrayed in a widely spaced checkerboard pattern. This provided the units both protection and greater freedom of movement.

The Romans marched into battle in disciplined ranks and files. Backing and flanking the centuries were archers and artillery, while slingers and skirmishers sallied forward to harass the enemy. Cavalry was employed to strike at a foe’s flanks and rear, while other troops were held in reserve. A commander could observe and control troop movements from behind the lines, dispatching orders to his officers. This was not an army of individual heroes hungry for glory but one of cohesion, precision and massive striking power. It was an offensive army taught to fight with great brutality, to destroy enemy forces and remove them as a threat, and to subjugate and ultimately assimilate their foes to expand the frontiers of Rome. It was the motive force behind the establishment of colonies from Britain to North Africa to Turkey.

Over time a legionary’s gear evolved from pre-hoplite to hoplite to manipular. Shield and helmet shape varied, as did body armor, but the two key weapons remained essentially the same. The primary weapon was the gladius, a short, heavy double-edged stabbing sword—“a descendant of the weapon of the Spanish Celts,” according to one weapons expert. The other was the pilum, a javelin with a needle-sharp point and thin iron shaft for maximum penetration. On his back the legionary carried a rucksack full of provisions, personal items and entrenching tools. The legions embarked on long campaigns of conquest not just raids for honor and vengeance.

When confronting the Celts, the Roman army approached in three ranks. Archers and artillery, slingers and skirmishers would strike the foe with a variety of projectiles, then the first ranks would throw their pila, aiming to kill, or at least to impale Celtic shields, making them unwieldy. With their swords drawn and shields locked in a solid wall, the Romans advanced or met the Celtic charge. While the Celts raised their long swords to strike downward, the Roman soldiers ducked behind their shields and stabbed at the enemy’s exposed abdomen, groin or legs. If a Celt went down, the Romans ruthlessly and quickly dispatched him. Meanwhile, the Roman cavalry attacked the enemy’s vulnerable flanks and slaughtered those attempting to flee.


Because of the freewheeling Celtic tendency to migrate to new lands, and the relentless surge of Roman expansion beyond the Italian peninsula, driven by economic and political factors, the civilizations’ were fated to encounter each other repeatedly—both on the battlefield and in the marketplace. Roman and Celtic businessmen engaged in a lively exchange of goods that included wine, tin, lead, silver, gold, salt and fine Mediterranean pottery. “All Gaul,” Roman philosopher and politician Cicero observed, “is filled with traders—is full of Roman citizens.” Some Celtic tribes formed alliances with Rome and fought in her armies; still others joined forces with Rome’s enemies. Other tribes became enamored of the Roman way of life—the prosperous cities and farms, the well-developed infrastructure and stable government—and became Romanized. Roman writers and artists idealized the Celts as “noble savages,” while many of the Celtic elite adopted the manners and style of the Roman aristocracy. Both cultures worshiped a pantheon of essentially similar gods, although Romans abhorred the Celtic practice of human sacrifice.

For ambitious Romans the prospect of the Celts’ fertile lands and rich gold and salt mines proved irresistible. They manipulated public dread of the “Gallic terror” to gain victories and territory for Rome while furthering their own careers. And thus the wars continued, especially those conceived by Caesar.

By the time of the great general’s decade-long conquest of Gaul (present-day France), culminating in the 52 BC Battle of Alesia, the Celts faced pressure from two other expansionist powers—the Germanic tribes to the north and Dacians to the east. As the Celtic tribes contracted westward, Caesar seized the opportunity to enhance his prestige and fortify his power base in Rome, while protecting and extending Roman economic interests in Gaul and allaying deep-seated Roman fears of “primitive” Celts bent upon destroying their civilization.

Caesar opened his conquest with an attack on the dominant Helvetii tribal confederation. In a series of brilliant campaigns he soon subdued the Gallic Celts and even briefly invaded Britain in 55 and 54 BC. Caesar came away boasting spectacular military successes to the people of Rome and portraying himself as their protector, even as most Celts simply wanted to be left alone, likely fearing the Germans more than the Romans.

But the fiery Celts complicated Caesar’s ambitious plans by continually revolting against Roman rule. Ultimately, a charismatic Celtic warlord named Vercingetorix, of the Arverni, united the Gallic tribes in resistance to the Romans. After a series of marches and engagements against Caesar, Vercingetorix’s forces retreated to a hill camp at Alesia (present-day central France), where they awaited the arrival of 8,000 cavalry and 240,000 infantry from allied tribes. Caesar’s forces comprised some 60,000 troops.

Undaunted, Caesar constructed two fortified walls— an inner one encircling Alesia, and an outer wall protecting his army from the Celtic relief force. This circumvallation enabled Caesar to seal off the hill camp and subdue the arriving Celts in detail. Witnessing the defeat of his relief force, Vercingetorix surrendered his forces to Caesar and was carted off to Rome for later ritual execution.

Caesar had won his war, but at a terrible price. “Of an estimated population of 6 to 7 million,” Celtic scholar Barry Cunliffe calculates, “about 1 million had been killed and another million sold into slavery. Among the remainder hardly a family would have been left unscarred. The resentment must have been deep and bitter.”

“What the [Romans] call ‘empire,’” contemporary Celtic chieftain Calgacus observed, “is theft and butchery; and what they call ‘peace’ is the silence of death.”

The last Celtic stronghold lay in the British Isles. The Celts there had been on good terms with the Romans since Caesar’s invasion, importing wine and exporting corn, hides and slaves to Rome. But in AD 43 Emperor Claudius, for a variety of economic, political and self-aggrandizing reasons, invaded Britain. He faced bitter resistance from the Celtic tribes. In 60 Celtic Queen Boudicca, of the Iceni, led a revolt against Roman rule, in part spurred by a Roman attack on an important Druid sanctuary on Anglesey. Boudicca’s forces wiped out several Roman settlements and troops before being crushed, with an estimated 80,000 killed. Imperial Roman power now extended to the Scottish border, where the 73-mile-long Hadrian’s Wall, begun in 122, partitioned the Roman and Celtic worlds, ending centuries of cross-cultural conflict.

Fierce and proud warriors, the Celts gradually succumbed to the Romans’ superior organizational skills and single-minded will to expand their empire. Ultimately, however, it was the Germanic tribes and a mystery religion from the east —Christianity—that transformed the Roman and Celtic ways forever. The Celts had made valuable contributions to Roman culture in warfare, technology and language, while the Romans had shared their material gifts, operational talents and political-urban lifestyle with the Celts. Both civilizations form the core of modern Europe. Yet the grandeur that was Rome survives only in crumbling marble ruins and a few magnificent texts. The Celtic way, however, thrives in the strongholds of Brittany, Galicia, Scotland, Cornwall, Wales and Ireland, as well as in a vigorous Celtic revival throughout Europe and North America. In the end it seems tribe has triumphed over empire.


O’Brien Browne is a contributing editor of Military History Quarterly. For further reading he suggests The Ancient Celts, by Barry Cunliffe; Roman Warfare, by Adrian Goldsworthy; and Romans and Barbarians, by Derek Williams.

Originally published in the January 2015 issue of Military History. To subscribe, click here.