Military of ancient Rome
The military of ancient Rome was one of the largest pre-modern professional standing armies in history. At its height, protecting over 7,000 kilometers of border and consisting of over 400,000 legionaries and auxiliaries, the army was the most important institution in the Roman world. According to the Roman historian Livy, the military was a key element in the rise of Rome over "above seven hundred years" from a small settlement in Latium to the capital of an empire governing a wide region around the shores of the Mediterranean, or, as the Romans themselves said, mare nostrum, "our sea". Livy asserts:
Titus Flavius Josephus, a contemporary historian, sometime high-ranking officer in the Roman army, and commander of the rebels in the Jewish revolt describes the Roman people as if they were "born readily armed". At the time of the two historians, Roman society had already evolved an effective military and had used it to defend itself against the Etruscans, the Italics, the Greeks, the Gauls, the maritime empire of Carthage, and the Macedonian kingdoms. In each war, it acquired more territory until, when the civil war ended the Roman Republic, nothing was left for the first emperor, Augustus, to do except declare it an empire and defend it.
The role and structure of the military were then altered during the empire. It became less Roman, the duties of border protection and territorial administration being more and more taken by foreign mercenaries officered by Romans. When they divided at last into warring factions the empire fell, unable to keep out invading armies.
During the Roman Republic, the function of the military was defined as service to the "Senatus Populusque Romanus" – an agency designated by SPQR on public inscriptions. Its main body was the senate, which met in a building still extant in the forum of Rome. Its decrees were handed off to the two chief officers of the state, the consuls. They could levy from the citizens whatever military force they judged was necessary to execute such decree. This conscription was executed through a draft of male citizens assembled by age class. The officers of the legion were tasked with selecting men for the ranks. The will of the SPQR was binding on the consuls and the men, with the death penalty often assigned for disobedience or failure. The men were under a rigorous code, known now for its punitive crucifixion.
The consular duties were of any type whatever: military defense, police work, public hygiene, assistance in a civil disaster, health work, agriculture, and especially the construction of public roads, bridges, aqueducts, buildings, and the maintenance of such. The soldiers were kept busy doing whatever service needed to be done: soldiering, manning vessels, carpentry, blacksmithing, clerking, etc. They were trained as required, but also previous skills, such as a trade, were exploited. They were brought to the task and were protected by the authority of the state.
The military's campaign history stretched over 1300 years and saw Roman armies campaigning as far east as Parthia, as far south as Africa and Aegyptus and as far north as Britannia. The makeup of the Roman military changed substantially over its history, from its early days as an unsalaried citizen militia to a later professional force, the Imperial Roman army. The equipment used by the military altered greatly in type over time, though there were very few technological improvements in weapons manufacture, in common with the rest of the classical world. For much of its history, the vast majority of Rome's forces were maintained at or beyond the limits of its territory, to either expand Rome's domain or protect its existing borders. Expansions were infrequent, as the emperors, adopting a strategy of fixed lines of defense, had determined to maintain existing borders. For that purpose, they constructed extensive walls and created permanent stations that became cities.
Personnel
Population base of the early empire
At its territorial height, the Roman Empire may have contained between 45 million and 120 million people. Historian Edward Gibbon estimated that the size of the Roman army "most probably formed a standing force of three hundred and seventy-five thousand men" at the empire's territorial peak in the time of the Roman emperor Hadrian. This estimate probably included only legionary and auxiliary troops of the Roman army. However, Gibbon states that it is "not... easy to define the size of the Roman military with any tolerable accuracy". In the late imperial period, when vast numbers of foederati were employed by the Romans, Antonio Santosuosso estimated the combined number of men in arms of the two Roman empires numbered closer to 700,000 in total, drawing on data from the Notitia Dignitatum. However, he notes that these figures were probably subject to inflation due to the practice of leaving dead soldiers "on the books" to continue to draw their wages and ration. Furthermore, it is irrespective of whether the troops were raised by the Romans or simply hired by them to fight on their behalf.Recruitment
Initially, Rome's military consisted of an annual citizen levy performing military service as part of their duty to the state. During this period, the Roman army prosecuted seasonal campaigns against largely local adversaries. As the extent of the territories falling under Roman suzerainty expanded, and the size of the city's forces increased, the soldiery of ancient Rome became increasingly professional and salaried. As a consequence, military service at the lower levels became progressively longer-term. Roman military units of the period were largely homogeneous and highly regulated. The army consisted of units of citizen infantry known as legions as well as non-legionary allied troops known as auxiliary. The latter were most commonly called upon to provide light infantry or cavalry support.Military service in the later empire continued to be salaried yearly and professionally for Rome's regular troops. However, the trend of employing allied or mercenary troops was expanded such that these troops came to represent a substantial proportion of Rome's forces. At the same time, the uniformity of structure found in Rome's earlier military forces disappeared. The soldiery of the era ranged from lightly armed mounted archers to heavy infantry, in regiments of varying size and quality. This was accompanied by a trend in the late empire of an increasing predominance of cavalry rather than infantry troops, as well as an emphasis on more mobile operations.
Military subculture
The British historian Peter Heather describes Roman military culture as being "just like the Marines, but much nastier". The army did not provide much social mobility, and it also took quite some time to complete one's service. The pay was not the best for the time but could be remedied by advance in rank, loot from wars, and additional pay from emperors. Also, the army did provide a guaranteed supply of food, doctors, and stability. In the legions of the Republic, discipline was fierce and training harsh, all intended to instill a group cohesion or esprit de corps that could bind the men together into effective fighting units. Unlike opponents such as the Gauls, who were fierce individual warriors, Roman military training concentrated on instilling teamwork and maintaining a level head over individual bravery − troops were to maintain exact formations in battle and "despise wild swinging blows" in favor of taking shelter behind one's shield and delivering efficient stabs when an opponent made himself vulnerable.Loyalty was to the Roman state but pride was based in the soldier's unit, to which was attached a military standard − in the case of the legions a legionary eagle. Successful units were awarded accolades that became part of their official name, such as the 20th Legion, which became the XX Valeria Victrix.
Of the martial culture of less valued units such as sailors, and light infantry, less is known, but it is doubtful that its training was as intense or its esprit de corps as strong as in the legions.
Literacy was highly valued in the Roman military, and literacy rates in the military far exceeded that of the Roman society as a whole.
Funding and expenditures
Private funding
Although early in its history, troops were expected to provide much of their equipment, eventually, the Roman military became almost entirely funded by the state. Since soldiers of the early republican armies were also unpaid citizens, the financial burden of the army on the state was minimal. However, since the Roman state did not provide services such as housing, health, education, social security, and public transport that are part and parcel of modern states, the military always represented by far the greatest expenditure of the state.Plunder economy
During the time of expansion in the Republic and early Empire, Roman armies had acted as a source of revenue for the Roman state, plundering conquered territories, displaying the massive wealth in triumphs upon their return and fuelling the economy to the extent that historians such as Toynbee and Burke believe that the Roman economy was essentially a plunder economy. Nathan Rosenstein has questioned this assumption, indicating that Rome ran the majority of its campaigns in the 2nd century BC at a loss and relied on rare windfalls such as Aemilius Paullus' campaign in the east in 168 BC to make up the cost of war. Regardless, after the empire had stopped expanding in the 2nd century AD, this source of revenue dried up; by the end of the 3rd century AD, Rome had "ceased to vanquish". As tax revenue was plagued by corruption and hyperinflation during the Crisis of the Third Century, military expenditures began to become a "crushing burden" on the finances of the Roman state. It now highlighted weaknesses that earlier expansion had disguised. By 440 AD, an imperial law frankly states that the Roman state has insufficient tax revenue to fund an army of a size required by the demands placed upon it.Several additional factors bloated the military expenditure of the Roman Empire. First, substantial rewards were paid to "barbarian" chieftains for their good conduct in the form of negotiated subsidies and the provision of allied troops. Secondly, the military boosted its numbers, possibly by one third in a single century. Third, the military increasingly relied on a higher ratio of cavalry units in the late empire, which were many times more expensive to maintain than infantry units.