This is a very brief account of the early development of the Roman Army, from its formation to its adoption by Augustus as an instrument of the Roman State. It is by no means exhaustive, and is intended merely as an introduction for those who have not yet studied this early period, and perhaps as an encouragement to do just that!
During the early centuries, the army of Rome was heavily influenced by the Etruscan Army, which in turn had learned and borrowed much from the Greek City States of Italy. The weapons and equipment were predominantly of Greek type and origin, and most battles were fought on foot, using the well tried and tested Greek 'phalanx'.
Recruitment was strictly based on citizenship and wealth. The assumption being that only a man with property to lose could be expected to defend it effectively, not to mention arming and equipping himself at his own expense. These citizens were in turn classified by their wealth into 5 classes of soldier. The wealthiest class formed the basis of the Legion, armed and equipped in the manner of a Greek hoplite. The remaining four classes made up the rest of the army in descending order of quality of arms and armour. Officers were selected from leading citizens, and enrolled into the Order of Knights, or Equites. Again at their own expense, but they were provided with a horse from the public purse. At this stage, the army was very much a defensive formation, called up as and when required.
In about 390BC, a massive Celtic invasion of Italy resulted in the sack and burning of Rome. The Roman Army proved totally unable to defend its city, and was easily swept aside. After the Celts departed with their spoils, it was obvious that a serious reorganisation was essential to prevent any such disaster in the future.
After some experimentation and evolution the Legion emerged as a battle formation of three individual but flexible and interactive lines of soldiers. Individually these were known as the Hastati, the Principes, and the Triarii.. The Hastati of the front line were the pick of the army. Young men, well trained and well armed with sword, javelin and large shield or scutum. The Principes behind them were older men, selected for their experience and maturity. Possibly the best equipped, they were armed and armoured similarly to the Hastati.
The Triarii of the third line were veterans, perhaps past their prime, but still well armed. There was also a fourth line of soldiers, known as the Velites. These came from the poorest class of citizens. Lightly armed with perhaps no more than a javelin and a light round shield, they were used as skirmishers to engage and perhaps draw the enemy onto the battle line proper. This task achieved, the Velites would rapidly withdraw to the rear through gaps left for them in the main battle line. The brunt of the attack was then absorbed by the Hastati, who either held their own, or if unable to do so, withdrew through the Principes. These now took up the fight, and if necessary in their turn withdrew through the Triarii, who then took up the fight. This situation was generally held to be a disaster. However, the one advantage of this system was that it did give the commander an opportunity to regroup his troops, and deploy them back into the battle line with fresh impetus, as and where required.
The above mentioned formations and methods carried Rome to eventual victory over Carthage in the Punic Wars. It was a close run thing at times, with Roman commanders often showing a remarkable if typical lack of imagination and flexibility. Hannibal quickly learned to exploit this weakness, and inflicted some crushing defeats on many Roman armies. Eventually the equally typical doggedness of the Romans was to prove decisive. The war was carried over to north Africa by the newly emerging Roman Navy, which ultimately proved superior to that of Carthage. The city was sacked, and Carthage as a power ceased to exist.
It was during this period that the Roman Army began to establish its own identity by the evolution of new battle tactics, and by adopting new weapons, often copied from their enemies. Celtic type helmets and mail shirts were adopted. The short Gladius Hispaniensis sword came from the Iberian peninsula, and both the large Scutum shield and the Pilum javelin seem to have been borrowed from other Italian tribes. By these methods, the army of Rome became the most powerful and efficient force in Italy.
It must be remembered that by threats and coercion, the Romans usually managed to enlist other neighbouring tribes to act as auxiliary troops. These 'allies' were not always happy with this arrangement, showing an increasing reluctance to send their young men to fight Rome's battles. This was eventually to result in much bloodshed, especially in the last century BC.
During the 1st century BC, Roman influence was to expand rapidly, initially eastwards, and finally culminating in Caesar's Gallic conquests. Naturally, this new 'empire' would demand more and more troops to maintain it, and to enable further expansion. Ironically, fresh levies of troops became available as a result of the extremely bloody 'Social' wars between Rome and the disenchanted Italian tribes. Though Rome prevailed, the result was a general extension of Roman citizenship to the other tribes. These new citizens became instantly eligible to serve in the Legions, and not just as 'Allied' irregulars or auxiliaries.
However, there being no funds to establish these new legions, it fell upon wealthy citizens to provide the necessaries. This resulted in many 'private' armies, dependent on their founder and not on the Roman State. The Dictator Sulla, is reputed to have been the first to instigate an oath of loyalty to himself by his soldiers. Perhaps for this reason the 1st. century BC produced some remarkable military figures. Marius, Sulla, Pompey and Caesar, to name but the most famous. Their personal ambitions inevitably led to conflict, and the resulting civil wars occupied much of this century. But the empire continued to expand as one or other of them pursued their ambitions overseas.
During this turbulent period, further fundamental changes occurred in the army. Most of these have been attributed to the great soldier and statesman, Gaius Marius, although many of these may already have been gradually evolving. What is undisputed is that Marius opened up his legions to the very lowest citizen class. Without property and wealth, these slum dwellers had always been excluded from a military career. As civil and other wars took their toll, Marius recruited unashamedly from the 'sweepings of the gutters of Rome'. He armed and equipped them at his own expense, and provided them with a thorough military training. Though derided by most of Roman society, Marius nevertheless had set a precedent, and thus established the very first professional army. Totally loyal to himself, of course.
The composition of the army also experienced another thorough revision during this period. The weapons and equipment of the legionary soldier were standardised, and the old distinctions between Hastati, Principes and Triarii were abolished. All legionary soldiers became the same, and were trained in a more flexible way of fighting. The main tactical formation became the Cohort, consisting of 6 Centuries of 80 men. There were 10 Cohorts to each Legion, giving a nominal strength of 4800 soldiers. The Legion became the focus of a soldiers' loyalty, under the sacred Eagle standard, also reputedly established by Marius.
After the battle of Actium, the victorious Octavian seized control of all Roman forces. He disbanded all surplus legions, retaining about 28, which he considered adequate for the defence of the Empire. Under the title of Augustus, he received a personal oath of loyalty from every unit of the Roman Army, thus ending a long period of strife and bloodshed.