TYPES OF UNITS
There were several different types of foot units; there were also three types of infantry. The first which were at the front lines were the Hastati. The Hastati were the youngest and least experienced of the Rome infantry. Being in the front lines meant that they suffered the most casualties. The Hastati had to buy their own equipment, but as soon as you surveyed the Hastati you were automatically promoted to the Principles. The Principles were the second line in battle in the army. They had better armor then the Hastatit. After this you were promoted to Triarii. The Triarii was the third line in battle. When the principles fell back the Triarii would be behind them reforming the line. Then they will counter attack. When they had long marches the Triarii were given a horse.
Archers
Roman archers did not necessarily play an important role in the Roman military warfare, but every part of the army had its role. Since there were no guns back then, archers shaped the military. The archers were the supporting troops for infantry. They were the secondary role in warfare. They had a lack of amour and poor hand weapons. Archers were recruited among peasants.
Cavalry
When you think of the word cavalry, you think of military men on horses. The Roman Empire did not put their cavalry on horses, actually Romans were not good horsemen. Their cavalry were back-up soldiers, and they were the weakest of all Roman soldiers. Members of the cavalry were archers and secondary foot soldiers. The archers were known as the Sagittarii and the foot soldiers were known as Lancearii. There were some cavalry units that were occupied by warriors that were well armored. The military group was well armored because they were a specialties division that specialized in counter attacking archers. The cavalry also had some of the first medics in war. These medics were known as Eques Sapsarius and they were the few that rode around on horseback. There were many other cavalry ranks but these were some of the main ones.