Martian Legio Comitatensis were and arguably are the backbone of martian military power, they are trained to operate in assaults both on the ground and in space. They are the offensive troopers of Mars and are trained to operate in small groups against greater numbers. They rely on individual initiative and bravery.
The armor provides life support and protection and a small amount of aid in targetting. The gun is powerful, even if antiquated and its underbarrel grenade launcher provides the legionary with a number of options in combat.
Legio Comitatensis means companion soldiers and one of their main tasks are to bodyguard important officials. Legio I: Sons of Mars is the famed bodyguard of the emperor himself and many emperors have originally been lords in Legio I.