Military history of the Roman Empire

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Soldiers reenacting the Roman Army on manoeuvres
Soldiers reenacting the Roman Army on manoeuvres

Rome was a militarized state whose history was often closely entwined with its military history over the 1228 years that the Roman state is traditionally said to have existed. The core of the military history of the Roman Empire is the account of its great land battles, from the conquest of Italy to its final battles against the Huns. This account may be divided into the Republic period, when Rome was primarily expansionist, and the Imperial period, when Rome focused on maintaining its borders.



See also Roman military structure.

Roman army

History and evolution

"Roman Army" is the name given to the sophisticated collection of soldiers and other military forces which served the Roman Republic and later the Roman Empire. The Army dominated much of the land surrounding the Mediterranean Sea, including the province of Britannia and Asia Minor at the Empire's height. Beginning as a citizen army, the Roman Army evolved into a professional army following the reforms of Gaius Marius around 100 BC.

Pre-Republican military evolution

Rome's first army was naught but a primitive and unorganized band of militia. They fought with whatever weapons they found most comfortable, and only the wealthiest would have worn armor or used weapons that didn't double as civilian implements (swords and spears have no purpose when not fighting). This force was unable to resist the Etruscan invasion of the late 7th century BC.

The Etruscans, having conquered Rome, expected her to contribute soldiers to their armies, and therefore imposed their method of military organization on the fledgling city. Under the Etruscan system, Rome's army was organized on the basis of social and economic standing. The upper half of men would form as hoplites in a phalanx, the combat formation traditionally used by Greek infantry. The class section directly below them would organize into a contingent of medium spearmen approximately 1/4 the size of the phalanx. The level below them served as light spearmen of similar size; below them, men fought as javelin-throwing skirmishers or slingers.

Rome continued to use this organizational system even after she overthrew Etruscan rule in 510 BC, though by 340 BC, Livy describes the army as drastically different.

The Republican Army

At any rate, Polybius describes the republican army at what is arguably its height in 160 BC. Serving in the army was part of civic duty in Rome. To be a legionaire (infantry) one had to meet a property requirement. They were divided into three groups, the Hastati, Principes, and Triarii, organized by age. The younger Hastati served in the front line, and were generally the least well armored, as they had little money to purchase such things.The Hastati and principes were by this time armed with a gladius (the spanish sword) and usually one or two javelins (pilum). The trairii were armed with spears, and traditionally formed the third line of the legion, usually crouching with their spears outward as a last ditch defense. As men gained experience and acumulated equipment they were moved into the other ranks. Each infantry man was part of a century of 80 men, two of which formed a maniple, the common unit of maneuver, 25-30 of which made up a legion. Those of the lowest classes, or too young to serve were in lightly armed skirmisher units and known as velites. The Roman upper-middle class, or Equites, were obligated to own horses, and hence served in the cavalry. The upper class of Rome, the Senators, served as the army's leaders, serving as legates and tribunes. All of these groups together formed a legion.

The overall command of legions in the early Republic was given to the two annually-elected consuls, which often led to mismanagement. Sometimes this even lead to them commanding the Roman forces on alternate days so neither would gain power over the other, resulting in more than one defeat. In the later republic, the relatively small number of legions commanded by the consuls (2-4) resulted in their power being overshadowed by the proconsuls, the provincial governors. They would often have more loyalty (eee Marian Reforms) from their troops than their consular counterparts, and the same time have the ability to raise vast numbers of troops. While the provincial armies were technically supposed to stay within the province their governor controlled, this was ignored by the middle of the 1st Century BC. By the end of the Republic, the various men involved in the civil wars had raised the number of legions throughout the Republic's provinces to more than fifty, many at the command of a single man.

Marian Reforms

By the end of the 2nd Century BC the Republican army was experiencing a severe manpower shortage. The extremely popular Gaius Marius at the end of that century used his power to reorganize the Republican army. Firstly, while still technically illegal, he recruited men from the lower classes who did not meet the official property requirement, a process originally started in the middle of the 2nd Century BC by the Grachhi. He also reorganized the legions into the now familar cohort system, doing away with the clumsy manipular system. Now legions were made up of 10 cohorts of 6 centuries of 80 apiece. The first cohort carried the new universal standard, a silver (later gold) eagle called the aquilia. This cohort had one less century, but each century had double the men of normal centuries, giving a total of approximately 4,800 men in each legion. These reforms are important for two reasons. One is from this point, legions began to become less and less a civic duty of the property owning classes, becoming almost entirely manned by the lower classes. Also, by eliminating the rather unwieldy three-line manipular system, a legion could now react more effectively to changes on the battlefield. Every infantry member of the legion now had the same arms (gladius) and were given supply packs, and as time went on the need to supply their own armour was eliminated in favour of the state supplying it. This is the real starting point of the Roman army's transition to a professional force.

Unfortunately, because it was the lower classes making up the legions, they now had to rely on the loot provide retirement capital. Initially the Senate was asked to supply public land to retired soldiers who had completed their terms of service, but it refused, and so these soldiers had to rely upon their generals to provide them for retirement. This was the driving force behind the civil wars that destroyed the Republic, as charismatic and successful generals such as Julius Caesar and Lucius Cornelius Sulla created personal loyalities over whatever loyalties those troops might have had to Rome.

The Imperial Army

During the reign of Augustus the army became a professional one. Its core of legionaires was composed of Roman citizens who served for a minimum of twenty five years. Augustus in his reign tried to eliminate the loyalty of the legions to the generals who commanded them, forcing them to take an oath of allegiance directly to him. While the legions remained relatively loyal to Augustus during his reign, under others, esspecially the more corrupt emperors or those who unwisely treated the military poorly, the legions often took power into their own hands. Legions continued to move farther and farther to the outskirts of society, esspecially in the later periods of the empire as the majority of legionaires no longer came from Italy, and were instead born in the provinces. The loyalty the legions felt to their emperor only degraded more with time, and lead in the 2nd Century and 3rd Century to a large number of military usurpers and civil wars. By the time of the military officer emperors that characterized the period following the Crisis of the Third Century the Roman army was just as likely to be attacking itself as an outside invader.

Both the pre- and post-Marian armies were greatly assisted by auxiliary troops. A typical Roman legion was accompanied by a matching auxiliary legion. In the pre-Marian army these auxiliary troops were Italians, and often Latins, from cities near Rome. The post-Marian army incorporated these Italian soldiers into its standard legions (as all Italians were Roman citizens after the Social War). Its auxiliary troops were made up of foreigners from provinces distant to Rome, who gained Roman citizenship after completing their twenty five years of service. This system of foreign auxiliaries allowed the post-Marian army to strengthen traditional weak points of the Roman system, such as light missile troops and cavalry, with foreign specialists, especially as the richer classes took less and less part of military affairs and the Roman army lost much of its domestic calvary.

At the beginning of the Imperial period the number of legions was 60, which Augustus more than halved to 28, numbering at approximately 160,000 men. As more territory was conquered throughout the Imperial period, this fluctuated into the mid-thirties. At the same time, at the beginning of the Imperial period the foreign auxiliaries made up a rather small portion of the military, but continued to rise, so that by the end of the period of the Five Good Emperors they probably equalled the legionaires in number, giving a combined total of between 300,000 and 400,000 men in the Army.

The last major reform of the Imperial Army came under the reign of Diocletian in the late 3rd Century. During the instability that had marked most of that century, the army had fallen in number and lost much of its ability to effectively police and defend the empire. He quickly recruited a large number of men, increasing the number of legionaires from between 150,000-200,000 to 350,000-400,000, effectively doubling the number in a case of quantity over quality.

Weapons and equipment

Roman navy

See main article, Roman Navy

History and evolution

The Roman navy was very much inferior, both in prestige and capability, to the Roman army. Before the First Punic War in 264 BC there was no Roman navy to speak of as all previous Roman war had been fought in Italy. But the war in Sicily against Carthage, a great naval power, forced Rome to quickly build a fleet and train sailors. The first few naval battles of the First Punic War were disasters for Rome, and it was not until the invention of the Corvus, a grappling engine which made it easier for Romans to board the Carthagenian vessels, that Rome was able to win the war. This meant that Rome could use her superior army in naval combat, and was a significant shift away from the tactics of all other navies at the time.

Rome was able to use her superior army in preference to her navy in most of the wars she fought afterwards. By the late Empire Roman control over the Mediterranean coast meant that there were no non-Roman navies to fight. Indeed, Rome's last major naval battle was fought between Romans, Octavian and Marc Antony, at Actium. However, she still maintained a large navy which patrolled not just the Mediterranean, but the various major rivers in the empire. Although the quality of the navy did degrade into the later imperial period, emperors such as Diocletian put significant effort into rebuilding the navy. The average estimate of manpower strength of the navy ranges from 50,000-100,000.

Weapons and equipment


Patterns of Roman wars

The first Roman wars were wars of expansion and defense, aimed at protecting Rome itself from neighboring cities and nations by defeating them in battle. This sort of warfare characterized the early Republican Period when Rome was focused on consolidating its position in Italy, and eventually conquering the peninsula. Rome first began to make war outside the Italian peninsula in the Punic wars against Carthage. These wars, starting in 264 BC saw Rome become a Mediterranean power, with territory in Sicily, North Africa, Spain, and, after the Macedonian wars, Greece. One important point that must be understood is that the Rome did not conquer most nations outright, at least as first, and instead forced them into a submissive position as allies and client states. These allies supplied men, money, and supplies to Rome against other opponents.

It wasn't until the late Republic that the expansion of the Republic started meaning actual annexation of large amounts of territory, however in this period, civil war became an increasingly common feature. In the last century before the common era at least 12 civil wars and rebellions occurred. These were generally started by one charismatic general who refused to surrender power to the Roman Senate, which appointed generals, and so had to be opposed by an army loyal to the Senate. This pattern did not break until Octavian, later Caeser Augustus ended it by becoming a successful challenger to the Senate's authority, and was crowned emperor.

As the emperor was a centralized authority with power focused in Rome, this gave both a benefit and weakness to expansion under the Roman Empire. Under powerful and secure emperors such as Augustus and Trajan great territorial gains were possible, but under weaker rulers such as Nero and Domitian weakness resulted in nothing more than usurption. One thing that all successful emperors had to accomplish was the loyalty of the legions throughout the empire. Weak emperors such as those relied upon generals to carry out their direct actions along the border, esspecially considering their requirement to stay in Rome to maintain power. This meant that often expansion in the empire came in leaps and bounds rather than a slow march. Another important point to remember is that many of the territories conquered in the imperial period were former client states of Rome whose regimes had degraded into instabiltiy, requiring armed intervention, often leading to outright annexation.

Unfortunately, the weakness of some emperors meant that these generals could wrest control of those legions away. The third century saw a crisis and a high number of civil wars similar to those that characterized the end of the Republic. Much like then, generals were wrestling control of power based upon the strength of the local legions under their command. Ironically, while it was these usurptions that lead to the break up of the Empire during that crisis, it was the strength of several frontier generals that helped reunify the empire through force of arms. Eventually, the dynastic structure of the imperial office returned due to the centralization of loyalty and control of the military once more, and then collapsed once again for the same reasons as before, leading to the destruction of the Western Half of the Empire. At this point, Roman military history becomes Byzantine military history.

List of Roman wars

See also List of Roman battles.

The list below is not exhaustive, but it does list the major wars that Rome fought, against both external and internal enemies. Famous Roman generals are listed along with the war that they are most closely associated with. Because many of these wars occurred within the life time of one man, and often simultaneously, several generals served in more than one of the wars listed. As well, famous enemies of Rome are listed in association with the war they fought in.

The wars themselves are organized into Wars of Conquest where Rome was seeking to exterminate an external enemy and/or guarantee its security against an external enemy, Revolts & Rebellions where Rome was being threatened by its own generals or by conquered peoples, and External Invasions where Rome fought an invasion by an external enemy without turning the war into one of conquest.

Wars of conquest

Revolts and rebelions

External invasions

See also

Template:Commonses:Ejrcito de la antigua Roma he:הצבא הרומי pt:Histria militar de Roma sl:Rimska vojska


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