The World of the Ancient Romans - Warfare

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Structural history

The structural history of the Roman military describes the major chronological transformations in the organization and constitution of the Roman armed forces. The Roman military was split into the Roman army and the Roman navy, although these two branches were less distinct than they tend to be in modern defence forces. Within the top-level branches of army and navy, structural changes occurred both as a result of positive military reform and through organic structural evolution.

Hoplite armies (509–c. 315 BC)

During this period, Roman armies seem to have been modelled after those of the Etruscans to the north, who themselves seem to have copied their style of warfare from the Greeks. Traditionally, the introduction of the phalanx formation into the Roman army is ascribed to the city's penultimate king, Servius Tullius (ruled 578 to 534 BC). According to Livy and Dionysius of Halicarnassus, the front rank was composed of the wealthiest citizens, who were able to purchase the best equipment. Each subsequent rank consisted of those with less wealth and poorer equipment than the one before it.


One disadvantage of the phalanx was that it was only effective when fighting in large, open spaces, which left the Romans at a disadvantage when fighting in the hilly terrain of central Italy. Sometime during the fourth century, the Romans abandoned the phalanx in favour of the more flexible manipluar formation. This change is sometimes attributed to Marcus Furius Camillus and placed shortly after the Gallic invasion of 390 BC; it is more likely, however, that they were copied from Rome's Samnite enemies to the south, possibly as a result of Samnite victories during the Second Samnite War (326 to 304 BC).

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Manipular legion (c. 315–107 BC)

During this period, an army formation of around 5,000 men (of both heavy and light infantry) was known as a legion. The manipular army was based upon social class, age and military experience. Maniples were units of 120 men each drawn from a single infantry class. The maniples were typically deployed into three discreet lines based on the three heavy infantry types.

Each first line maniple were leather-armoured infantry soldiers who wore a brass breastplate and a brass helmet adorned with 3 feathers approximately 30 cm (12 in) in height and carried an iron-clad wooden shield. They were armed with a sword and two throwing spears. The second infantry line was armed and armoured in the same manner as was the first infantry line. The second infantry line, however, wore a lighter coat of mail rather than a solid brass breastplate. The third infantry line was the last remnant of the hoplite-style (the Greek-style formation used occasionally during the early republic) troops in the Roman army. They were armed and armoured in the same manner as were the soldiers in the second line, with the exception that they carried a lighter spear.


The three infantry classes may have retained some slight parallel to social divisions within Roman society, but at least officially the three lines were based upon age and experience rather than social class. Young, unproven men would serve in the first line, older men with some military experience would serve in the second line, and veteran troops of advanced age and experience would serve in the third line.

The heavy infantry of the maniples were supported by a number of light infantry and cavalry troops, typically 300 horsemen per manipular legion. The cavalry was drawn primarily from the richest class of equestrians. There was an additional class of troops who followed the army without specific martial roles and were deployed to the rear of the third line. Their role in accompanying the army was primarily to supply any vacancies that might occur in the maniples. The light infantry consisted of 1,200 unarmoured skirmishing troops drawn from the youngest and lower social classes. They were armed with a sword and a small shield, as well as several light javelins.

A small navy had operated at a fairly low level after about 300 BC, but it was massively upgraded about forty years later, during the First Punic War. After a period of frenetic construction, the navy mushroomed to a size of more than 400 ships on the Carthaginian ("Punic") pattern. Once completed, it could accommodate up to 100,000 sailors and embarked troops for battle. The navy thereafter declined in size. The extraordinary demands of the Punic Wars, in addition to a shortage of manpower, exposed the tactical weaknesses of the manipular legion, at least in the short term. In 217 BC, near the beginning of the Second Punic War, Rome was forced to effectively ignore its long-standing principle that its soldiers must be both citizens and property owners. During the second century BC, Roman territory saw an overall decline in population, partially due to the huge losses incurred during various wars. This was accompanied by severe social stresses and the greater collapse of the middle classes. As a result, the Roman state was forced to arm its soldiers at the expense of the state, which it had not had to do in the past.

The distinction between the heavy infantry types began to blur, perhaps because the state was now assuming the responsibility of providing standard-issue equipment. In addition, the shortage of available manpower led to a greater burden being placed upon Rome's allies for the provision of allied troops. Eventually, the Romans were forced to begin hiring mercenaries to fight alongside the legions.

The legion after the reforms of Gaius Marius (107 BC – 27 BC)

In a process known as the Marian reforms, Roman consul Gaius Marius carried out a programme of reform of the Roman military. In 107 BC, all citizens, regardless of their wealth or social class, were made eligible for entry into the Roman army. This move formalised and concluded a gradual process that had been growing for centuries, of removing property requirements for military service. The distinction between the three heavy infantry classes, which had already become blurred, had collapsed into a single class of heavy legionary infantry. The heavy infantry legionaries were drawn from citizen stock, while non-citizens came to dominante the ranks of the light infantry. The army's higher-level officers and commanders were still drawn exclusively from the Roman aristocracy


Unlike earlier in the Republic, legionaries were no longer fighting on a seasonal basis to protect their land. Instead, they received standard pay, and were employed by the state on a fixed-term basis. As a consequence, military duty began to appeal most to the poorest sections of society, to whom a salaried pay was attractive. A destabilising consequence of this development was that the proletariat "acquired a stronger and more elevated position" within the state.

The legions of the late Republic were, structurally, almost entirely heavy infantry. The legion's main sub-unit was called a cohort and consisted of approximately 480 infantrymen. The cohort was therefore a much larger unit than the earlier maniple sub-unit, and was divided into six centuries of 80 men each. Each century was separated further into 10 "tent groups" of 8 men each. Legions additionally consisted of a small body, typically 120 men, of Roman legionary cavalry. The cavalry troops were used as scouts and dispatch riders rather than battlefield cavalry. Legions also contained a dedicated group of artillery crew of perhaps 60 men. Each legion was normally partnered with an approximately equal number of allied (non-Roman) troops.

However, the most obvious deficiency of the Roman army remained its shortage of cavalry, especially heavy cavalry. As Rome's borders expanded and its adversaries changed from largely infantry-based to largely cavalry-based troops, the infantry-based Roman army began to find itself at a tactical disadvantage, particularly in the East.

After having declined in size following the subjugation of the Mediterranean, the Roman navy underwent short-term upgrading and revitalisation in the late Republic to meet several new demands. Under Caesar, an invasion fleet was assembled in the English Channel to allow the invasion of Britannia; under Pompey, a large fleet was raised in the Mediterranean Sea to clear the sea of Cilician pirates. During the civil war that followed, as many as a thousand ships were either constructed or pressed into service from Greek cities.

Campaign history

The core of the campaign history of the Roman Republican military is the account of the Roman military's land battles. Despite the encompassing of lands around the periphery of the Mediterranean sea, naval battles were typically less significant than land battles to the military history of Rome.

As with most ancient civilisations, Rome's military served the triple purposes of securing its borders, exploiting peripheral areas through measures such as imposing tribute on conquered peoples, and maintaining internal order. From the outset, Rome's military typified this pattern and the majority of Rome's campaigns were characterised by one of two types. The first is the territorial expansionist campaign, normally begun as a counter-offensive, in which each victory brought subjugation of large areas of territory. The second is the civil war, of which examples plagued the Roman Republic in its final century.


Roman armies were not invincible, despite their formidable reputation and host of victories. Over the centuries the Romans "produced their share of incompetents" who led Roman armies into catastrophic defeats. Nevertheless, it was generally the fate of even the greatest of Rome's enemies, such as Pyrrhus and Hannibal, to win the battle but lose the war. The history of Rome's campaigning is, if nothing else, a history of obstinate persistence overcoming appalling losses.

Roman expansion into Italia (343-282 BC)

After recovering surprisingly swiftly from the sack of Rome, the Romans immediately resumed their expansion within Italy. The First Samnite War of between 343 BC and 341 BC was a relatively short affair: the Romans beat the Samnites in two battles, but were forced to withdraw from the war before they could pursue the conflict further due to the revolt of several of their Latin allies in the Latin War. Rome bested the Latins in the Battle of Vesuvius and again in the Battle of Trifanum, after which the Latin cities were obliged to submit to Roman rule.

The Second Samnite War, from 327 BC to 304 BC, was a much longer and more serious affair for both the Romans and Samnites. The fortunes of the two sides fluctuated throughout its course. The Romans then proved victorious at the Battle of Bovianum and the tide turned strongly against the Samnites from 314 BC onwards, leading them to sue for peace with progressively less generous terms. By 304 BC the Romans had effectively annexed the greater degree of the Samnite territory, founding several colonies.

Seven years after their defeat, with Roman dominance of the area looking assured, the Samnites rose again and defeated a Roman army in 298 BC, to open the Third Samnite War. With this success in hand they managed to bring together a coalition of several previous enemies of Rome. In the Battle of Populonia in 282 BC Rome finished off the last vestiges of Etruscan power in the region.

Pyrrhic War (280-275 BC)

By the beginning of the third century, Rome had established itself as a major power on the Italian Peninsula, but had not yet come into conflict with the dominant military powers in the Mediterranean at the time: Carthage and the Greek kingdoms

When a diplomatic dispute between Rome and a Greek colony erupted into open warfare in a naval confrontation, the Greek colony appealed for military aid to Pyrrhus, ruler of the northwestern Greek kingdom of Epirus. Motivated by a personal desire for military accomplishment, Pyrrhus landed a Greek army of some 25,000 men on Italian soil in 280 BC.

Despite early victories, Pyrrhus found his position in Italy untenable. Rome steadfastly refused to negotiate with Pyrrhus as long as his army remained in Italy. Facing unacceptably heavy losses with each encounter with the Roman army, Pyrrhus withdrew from the peninsula. In 275 BC, Pyrrhus again met the Roman army at the Battle of Beneventum. While Beneventum was indecisive, Pyrrhus realised his army had been exhausted and reduced, by years of foreign campaigns, and seeing little hope for further gains, he withdrew completely from Italy.

The conflicts with Pyrrhus would have a great effect on Rome. Rome had shown it was capable of pitting its armies successfully against the dominant military powers of the Mediterranean, and that the Greek kingdoms were incapable of defending their colonies in Italy and abroad. Rome quickly moved into southern Italia, subjugating and dividing the Greek colonies. Now, Rome effectively dominated the Italian peninsula, and won an international military reputation.

Punic Wars (264-146 BC)

The First Punic War began in 264 BC when settlements on Sicily began to appeal to the two powers between which they lay - Rome and Carthage - in order to solve internal conflicts. The war saw land battles in Sicily early on, but the theatre shifted to naval battles around Sicily and Africa. Before the First Punic War there was no Roman navy to speak of. The new war in Sicily against Carthage, a great naval power, forced Rome to quickly build a fleet and train sailors.

The first few naval battles were catastrophic disasters for Rome. However, after training more sailors and inventing a grappling engine, a Roman naval force was able to defeat a Carthaginian fleet, and further naval victories followed. The Carthaginians then hired Xanthippus of Carthage, a Spartan mercenary general, to reorganise and lead their army. He managed to cut off the Roman army from its base by re-establishing Carthaginian naval supremacy. With their newfound naval abilities, the Romans then beat the Carthaginians in naval battle again at the Battle of the Aegates Islands and leaving Carthage without a fleet or sufficient coin to raise one. For a maritime power the loss of their access to the Mediterranean stung financially and psychologically, and the Carthaginians sued for peace.

Continuing distrust led to the renewal of hostilities in the Second Punic War when Hannibal Barca attacked a Spanish town, which had diplomatic ties to Rome. Hannibal then crossed the Italian Alps to invade Italy. Hannibal's successes in Italy began immediately, and reached an early climax at the Battle of Cannae, where 70,000 Romans were killed.

In three battles, the Romans managed to hold off Hannibal but then Hannibal smashed a succession of Roman consular armies. By this time Hannibal's brother Hasdrubal Barca sought to cross the Alps into Italy and join his brother with a second army. Hasdrubal managed to break through into Italy only to be defeated decisively on the Metaurus River. Unable to defeat Hannibal himself on Italian soil, the Romans boldly sent an army to Africa with the intention of threatening the Carthaginian capital. Hannibal was recalled to Africa, and defeated at the Battle of Zama.


Carthage never managed to recover after the Second Punic War and the Third Punic War that followed was in reality a simple punitive mission to raze the city of Carthage to the ground. Carthage was almost defenseless and when besieged offered immediate surrender, conceding to a string of outrageous Roman demands. The Romans refused the surrender, and the city was stormed after a short siege and completely destroyed. Ultimately, all of Carthage's North African and Spanish territories were acquired by Rome.

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Macedon, the Greek poleis, and Illyria (215-148 BC)

Rome's preoccupation with its war with Carthage provided an opportunity for Philip V of the kingdom of Macedon, located in the north of Greece, to attempt to extend his power westward. Philip sent ambassadors to Hannibal's camp in Italy, to negotiate an alliance as common enemies of Rome. However, Rome discovered the agreement when Philip's emissaries were captured by a Roman fleet. The First Macedonian War saw the Romans involved directly in only limited land operations, but they ultimately achieved their objective of pre-occupying Philip and preventing him from aiding Hannibal.

Macedon began to encroach on territory claimed by Greek city states in 200 BC and these states pleaded for help from their newfound ally Rome. Rome gave Philip an ultimatum that he must submit Macedonia to being essentially a Roman province. Philip refused, and Rome declared war against Philip in the Second Macedonian War. Ultimately, in 197 BC, the Romans defeated Philip at the Battle of Cynoscephalae, and Macedonia was forced to surrender.

Rome now turned its attentions to one of the Greek kingdoms, the Seleucid Empire, in the east. A Roman force defeated the Seleucids at the Battle of Thermopylae and forced them to evacuate Greece. The Romans then pursued the Seleucids beyond Greece, beating them in the decisive engagement of the Battle of Magnesia.

In 179 BC Philip died and his talented and ambitious son, Perseus, took his throne and showed a renewed interest in Greece. Rome declared war on Macedonia again, starting the Third Macedonian War. Perseus initially had greater military success against the Romans than his father. However, as with all such ventures in this period, Rome responded by simply sending another army. The second consular army duly defeated the Macedonians at the Battle of Pydna in 168 BC and the Macedonians duly capitulated, ending the Third Macedonian War.

The Fourth Macedonian War, fought from 150 BC to 148 BC, was the final war between Rome and Macedon. The Romans swiftly defeated the Macedonians at the Second battle of Pydna. Another Roman army besieged and destroyed Corinth in 146 BC, which led to the surrender and thus conquest of Greece.

Caesar's early campaigns (59-50 BC)

During a term as praetor in Iberia (modern Spain), Pompey's contemporary Julius Caesar defeated two local tribes in battle. Following his term as consul in 59 BC, he was then appointed to a five year term as the proconsular Governor of Cisalpine Gaul (current northern Italy), Transalpine Gaul (current southern France) and Illyria (the modern Balkans). Not content with an idle governorship, Caesar strove to find reason to invade Gaul, which would give him the dramatic military success he sought. When two local tribes began to migrate on a route that would take them near (not into) the Roman province of Transalpine Gaul, Caesar had the barely sufficient excuse he needed for his Gallic Wars, fought between 58 BC and 49 BC.

Caesar defeated large armies at major battles 58 BC and 57 BC. In 55 and 54 BC he made two expeditions into Britain, becoming the first Roman to do so. Caesar then defeated a union of Gauls at the Battle of Alesia, completing the Roman conquest of Transalpine Gaul. By 50 BC, the entirety of Gaul lay in Roman hands. Gaul never regained its Celtic identity, never attempted another nationalist rebellion, and remained loyal to Rome until the fall of the western empire in 476.

Triumvirates and Caesarian ascension (53-30 BC)

By 59 BC an unofficial political alliance known as the First Triumvirate was formed between Gaius Julius Caesar, Marcus Licinius Crassus, and Gnaeus Pompeius Magnus ("Pompey the Great") to share power and influence. In 53 BC, Crassus launched a Roman invasion of the Parthian Empire (modern Iraq and Iran). After initial successes, he marched his army deep into the desert; but here his army was cut off deep in enemy territory, surrounded and slaughtered at the Battle of Carrhae in which Crassus himself perished. The death of Crassus removed some of the balance in the Triumvirate and, consequently, Caesar and Pompey began to move apart. While Caesar was fighting in Gaul, Pompey proceeded with a legislative agenda for Rome that revealed that he was at best ambivalent towards Caesar and perhaps now covertly allied with Caesar's political enemies. In 51 BC, some Roman senators demanded that Caesar not be permitted to stand for consul unless he turned over control of his armies to the state, which would have left Caesar defenceless before his enemies. Caesar chose Civil War over laying down his command and facing trial.

By the spring of 49 BC, the hardened legions of Caesar crossed the river Rubicon and swept down the Italian peninsula towards Rome, while Pompey ordered the abandonment of Rome. Afterwards Caesar turned his attention to the Pompeian stronghold of Iberia (modern Spain) but decided to tackle Pompey himself in Greece. Pompey initially defeated Caesar, but failed to follow up on the victory, and was decisively defeated at the Battle of Pharsalus in 48 BC, despite outnumbering Caesar's forces two to one, albeit with inferior quality troops. Pompey fled again, this time to Egypt, where he was murdered.


Pompey's death did not result in an end to the civil war as Caesar's enemies were manifold and continued to fight on. In 46 BC Caesar lost perhaps as much as a third of his army, but ultimately came back to defeat the Pompeian army of Metellus Scipio in the Battle of Thapsus, after which the Pompeians retreated yet again to Iberia. Caesar then defeated the combined Pompeian forces at the Battle of Munda.

Caesar was now the primary figure of the Roman state, enforcing and entrenching his powers and his enemies feared that he had ambitions to become an autocratic ruler. Arguing that the Roman Republic was in danger a group of senators hatched a conspiracy and murdered Caesar in the Senate in March of 44 BC. Mark Antony, Caesar's lieutenant, condemned Caesar's assassination, and war broke out between the two factions. Antony was denounced as a public enemy, and Caesar's adopted son and chosen heir, Gaius Octavian, was entrusted with the command of the war against him. At the Battle of Mutina Antony was defeated by the consuls Hirtius and Pansa, who were both killed.

Octavian came to terms with Caesarians Antony and Lepidus in 43 BC when the Second Triumvirate was formed. In 42 BC Triumvirs Mark Antony and Octavian fought the Battle of Philippi with Caesar's assassins Brutus and Cassius. Although Brutus defeated Octavian, Antony defeated Cassius, who committed suicide. Brutus joined him shortly afterwards.

However, civil war flared again when the Second Triumvirate of Octavian, Lepidus and Mark Antony failed. The ambitious Octavian built a power base of patronage and then launched a campaign against Mark Antony. At the naval Battle of Actium off the coast of Greece, Octavian decisively defeated Antony and Cleopatra. Octavian was granted a series of special powers including sole "imperium" within the city of Rome, permanent consular powers and credit for every Roman military victory, since all future generals were assumed to be acting under his command. In 27 BC Octavian was granted the use of the names "Augustus" and "Princeps" indicating his primary status above all other Romans, and he adopted the title "Imperator Caesar" making him the first Roman Emperor.

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Source: Wikipedia

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