Since the time of the Roman Legions, the armies were different from war bands for their organization and combat discipline. For example, specific structures grouped all the fighters on foot or on horseback and, according to the armament they were deployed for the battle. Moreover, special units provided to logistic needs that were necessary for the fighters.
As a consequence, "Armies" and "Corps" have been constituted. The Italian Army has got six Armies (Infantry, Cavalry, Artillery, Engineer, Signals, Transports and Materials) and three Corps (Medical, Administrative and Engineer).
The Armies and Corps are divided into "specialty" that correspond to the type of battle that each unit can support and that they are prepared for.