1. The Roman Army Roman Republican Army (from c. 300 – 107 BC)
The earliest Roman army was based originally on the Greek Phalanx system, and the Legion system continued to evolve from that origin, and from elements of Latin tribes in Italy.
The Roman Army
By the time the Romans began to resist Etruscan rule, the unique Legionary System was firmly rooted The Romans abandoned the use of the hoplite spear as its primary weapon of war and instead moved onto the large shield (scutum) and short sword (gladius) as their weapons, and corresponding tactics of choice.
The most significant difference between the Republican and Imperial Legions dealt with its makeup of social and financial qualifications. Except for certain circumstances where the very survival of Rome depended on using anyone available for defence, the Republican Legion maintained a strict social hierarchy. Only landowning citizens, ideally, were allowed to serve, and the status of one's total wealth along with military experience determined their place in the infantry. As each citizen (in the early Republican army) provided weapons and equipment from their own estates, gear could vary, but there was a basic uniform code to be followed within reason. This system was devised out of necessity, but perhaps incorporating the concept of loyalty to the city and morale of the men. Since the army was made up of citizens who could afford their own armour, they were the obvious choice for service. However, in the earliest days, the common concept that only the land owners had a real stake in the outcome of the battle likely played a key role in the development of the early Roman Legion.
Imperial Roman Army (30 BC – 284 AD)

2. Each rung of the ladder on the status of a soldier was based on his ability to equip himself. There is some debate, however on the social mobility of the legion ranks. Beyond the lowest orders, its quite likely that status of wealth may have allowed a citizen to move into a different rank class within the army.
It's far more likely that experience was the more determining factor in deciding a soldier's promotional within a legion after the initial status was determined. Once an army veteran was 're-enlisted' his class within the army was based again upon his wealth, but also age and experience.
A soldier within the Republican Legion served much the same as those within the Imperial one. They were eligible for service for a 20 year period and were retired or exempted from further service after that point. Unlike the Imperial army, however, the earlier Republic didn't maintain a standing army so to speak, and soldiers may or may not be entirely active during this time period. In some cases, such as during the Punic Wars (a series of wars between Rome and Carthage), a single soldier may have seen nearly continual service throughout his 20 year eligibility, but at others, he may have had give only periodic service based on the need for the army. Though the Romans rarely had a time of complete peace throughout their history, there were times when it was conceivable that these citizen soldiers could spend a great deal of time working their own lands.
THE EARLY YEARS OF POMPEY – Pompey, along with his father, fought in the Roman Civil War, raising three legions and was later sent to destroy the rebels in Africa and Sicily. On his triumphant return to Rome he was honoured with the title Magnus, or ‘the Great’. Pompey subsequently defeated a further rebellion and, upon returning to Italy, brought an end to the war instigated by the slave Spartacus. He was now the idol of the people and was elected consul (there were only two consuls elected a year) for 70 BC, serving with Crassus. In BC, he cleared the Mediterranean Sea of pirates and was given control of the provinces in the east. He conquered further territory and on his return to Italy he disbanded his army and in 61 BC entered Rome in triumph for the third time.