Roman Imperial Army
The Romans had a certain knack of organizing themselves. Then, they best organized themselves in the army. The Roman Army and the later Roman Imperial Army have a long and checkered history. The reign of the Roman Classical Army started 250 CE which later developed into the Roman Imperial Army. Earlier than the start of the Roman Imperial Army, the Roman Army had only Romans in it. However, the third century Roman emperors were embattled. Accordingly, they started recruiting any soldiers and armies that they could even the non-Roman military forces. Then, in the Roman Imperial Army, they recruited Germans, Arabs, Persians, Sarmatians, Armenians, and even the Moors. So, these worked as the Auxiliaries and were still not subjects of the Roman Empire.
The Roman Imperial Army
The legions of the Roman empire were not at all threatened by the new drafting that was occurring in the Roman Imperial Army. These new additions were part of the barbarian Imperial forces that continued to grow throughout the third century. Emperor Gallienus set the trend of increasing the cavalry and using only a small infantry legion. After this, the tradition set by Gallienus continued unabated in the Roman Imperial Army. This also brought a declining interest in the legions as the preferred cohorts of the Roman Imperial Army.
The third century was not beneficial for the Roman Imperial Army and the Emperor Diocletian started to reform it considerably. He also knew the main weakness of the Roman Imperial Army which was that starting with Augustus the Army was solely concentrated at the borders of the empire. Then, previously there was no Army in the central region of the Roman empire.
The Roman Imperial Army was a feat of great organization in the history of the world. Nowhere and at no time in world history has there been a bigger and more elite Army than the Roman Imperial Army. It started as a regular Roman Army. However, during the third century, the Roman emperors started to recruit other non-Roman armies in the regiment. This created a barbarian Imperial army which was unmatched by any other army of the time or even in history. The purpose was to serve the Roman emperor rather than anyone else. Then, many changes and reforms were introduced in the Roman Imperial Army that only made it stronger and more invincible.