How Rome Conquered the Mediterranean

After the overthrow of Tarquinius Superbus in 509 BCE ended a monarchy that tradition dated to Rome’s founding in 753 BCE, the young republic found itself surrounded by rival tribes and city-states. Over the next five centuries, it grew from a vulnerable city into an empire that encircled the Mediterranean Sea. Three factors drove that rise: a culture built around war, the effectiveness of the Roman legions, and Rome’s ability to absorb the peoples it conquered.

Depiction of the Roman Army. The Romans built their culture around military life early on. Men were expected to serve both as a civic duty and as a path to social advancement, and nearly every year Rome raised armies from its male citizens, who were bound by law and custom to answer the call. Most political leaders began their careers as soldiers and officers, and even the consuls who led the republic spent most of their time on campaign.

At the core of a Roman man’s identity was virtus. Unlike the modern idea of virtue, which is closely tied to goodness, virtus meant displaying masculine qualities: fighting in the legions when called, keeping a body strong enough to protect family and community, putting Rome above personal interest, and submitting to orders for the good of the whole. It was further expressed through four traits: pietas (dutifulness), fides (faith), gravitas (gravity), and constantia (constancy).

A virtuous man gained dignitas (honor, esteem), auctoritas (respect), and gloria (glory), and he climbed the social and political ladder as a result. Military service was the surest way to prove that virtue. The ideal Roman was a citizen soldier rather than a professional, a man who left his farm or trade to fight for Rome.

A relief of a battle scene between Roman legionaries and Germanic warriors. Image credit: Cris Foto / Shutterstock.com In the early and middle republic, legions were levied from the population through a process called the dilectus. Soldiers paid for their own equipment, so they were sorted into infantry roles according to what they could afford. The poorest became velites, lightly armed troops who fought at the front and threw javelins at the enemy ranks. Behind them stood three lines of better-equipped heavy infantry, often older and more experienced: the hastati, principes, and triarii. As a battle wore on, the later lines moved forward, letting Rome exhaust its enemies with its weakest soldiers before sending in its best.

Rome originally organized its men in the Greek phalanx. While fighting the Samnites, a neighboring Italian tribe, from the mid-300s to the 290s BCE, the Romans realized they needed armies that could maneuver through the hilly terrain of central Italy. The legions were reorganized into maniples, groups 12 legionaries wide and 10 men deep, arranged in a checkerboard pattern. The gaps let an exhausted front line fall back while the second line advanced, or let the front retreat into a more fortified line.

Gaius Marius as victor over the invading Cimbri. Credit: Francesco Saverio Altamura, Public domain, via Wikimedia Commons Late in the 2nd century BCE, the Roman statesman and general Gaius Marius abandoned the maniple for the cohort, which joined three maniples, one from each line, into a single unit. The separate infantry types were dissolved, and every legionary now served as heavy infantry. This increased unit cohesion and let the whole force fight at once when needed, rather than in stages.

To support the shift, Marius opened enlistment to landless citizens, who were equipped by the state, beginning the professionalization of the army. Soldiers also carried more of their own gear, reducing reliance on supply trains. The result was a disciplined force that fought as a cohesive unit and was trained to adapt quickly, ready to change strategy, adopt a new formation, or hold fast as a battle turned. The reformed legions would fight one another in Rome’s civil wars before turning on the remaining powers around the Mediterranean.

A mosaic from a Roman villa at Sidi Ghrib, in present-day Tunisia. Credit: Fabien Dany via Wikimedia Commons (CC BY-SA 2.5) The Romans were more than conquerors; they were experts at folding new provinces into their own culture. Where they could, they sought out cooperative local rulers and turned them against their countrymen, forming alliances that supplied soldiers or logistical support while dividing groups that might otherwise unite against Roman rule.

After a conquest, Roman leaders often encouraged the construction of temples, homes, public squares, and bathhouses. Young aristocrats were educated like Roman aristocrats, taught Latin, and introduced to Roman fashion and pastimes such as baths and dinner parties. In theory, citizenship could be granted to anyone regardless of nationality, and Rome dangled that prize, along with Roman culture, in front of locals who had resisted invasion and willing allies alike. Some territories were left as client kingdoms, puppet states that deferred to Rome. In exchange for sponsoring Roman culture, parts of their populations would eventually be granted citizenship.

Vercingetorix, a Gallic chieftain, surrenders to Julius Caesar. Image credit: Lionel Royer, Public domain, via Wikimedia Commons Integration was not always peaceful. When a territory held out or its people resisted, the Romans turned to force, and much of their conquest relied on the systematic extermination and enslavement of their enemies’ men, women, and children.Those who defied Rome were massacred or expelled: men who fought back were executed, and the remaining men, women, and children were sold as slaves in other provinces. Rome laid waste to the cities and estates of the conquered land and resettled it with its own people. Even this brutality fed integration over time. Some of the enslaved eventually earned their freedom, and their families could even obtain citizenship, drawing still more peoples into Roman society.

Trajan’s Column shows Roman leaders and cavalry assembling near a fort. Image credit: History Skills via Shutterstock The Romans also used the legions to integrate new peoples. Under the empire, men from conquered territories could serve a term, typically 25 years, as auxiliaries supporting the legionaries. They fought as front-line soldiers, archers, and cavalry, manned forts, and protected the borders. Auxiliaries often held the most dangerous posts in the army and were paid less than full legionaries. In return, they were rewarded with Roman citizenship and all the rights and privileges that came with it. Service also immersed conquered peoples in the martial culture and values of Rome. Because auxiliaries usually served far from their homelands, the system built a cosmopolitan society while preventing them from leading rebellions or wars of independence.

Closing of the Temple of Janus by Augustus. Image credit: Louis de Silvestre, Public domain, via Wikimedia Commons Roman society placed great weight on honor and justice in warfare. Just as a man should not instigate a fight, Rome was reluctant to start an unjust war. At least nominally, it fought only “just wars,” meaning wars of self-defense, fought only when necessary and never as the aggressor. In practice, pragmatism, greed, or anger often won out. The Romans constantly found excuses to declare just wars, goading enemies into a move, prodding them to attack an ally, or finding an injustice to avenge. Rome was not wrong every time: some foreign powers held territory or resources that would greatly benefit Rome, and some rivals posed a serious threat. Still, to treat Rome as always on the defensive is to accept its own propaganda uncritically. Like any nation, Rome fought both just and unjust wars on its way to its goals.

The Great Roman Empire Rome’s rise began at home, with a series of wars that secured its position in Italy. Between the early 5th century BCE and the early 3rd century BCE, it established firm control over the Italian Peninsula. Along the way, it defeated the Etruscans, Veientes, Gauls, Latins, and Samnites, and repelled an invasion by the Greek king Pyrrhus of Epirus.

By the end of the 1st century BCE, Rome’s borders encompassed nearly the whole Mediterranean, spanning the lands between the Iberian Peninsula and Egypt. Rome had conquered and begun to integrate Greece, Illyria (the modern-day western Balkans), Anatolia (modern-day Turkiye), Egypt, Spain, Gaul (modern-day France), Carthage (modern-day Tunisia and North Africa), and Syria. A few pockets still held out, but the outline of Rome’s empire had finally been traced.