The formation of the institution of a standing army under Augustus was a turning point in all subsequent Roman history. Very soon it became obvious that the security of the empire required a larger armed force. The main obstacles to the creation of new legions were financial difficulties. The high salaries of legionnaires and the inability to provide veterans with the full amount of support they were entitled to put the government in front of an almost insoluble dilemma: how to reduce the cost of maintaining troops without compromising the defense capability of the state. Nevertheless, while the neighbors of the Romans in the west were the fragmented tribes of the Germans, who were always at war with each other, and in the east - the Parthians, clashes with whom were episodic, the military system that developed under Augustus functioned, by and large, properly. Unfavorable foreign policy situation led to an increase in crisis phenomena throughout the Roman military organization. The crisis that shook the Roman world in the 3rd century was purely military in nature and was caused by the inability of the Roman military machine to function effectively in changed political conditions. How successful were the military reforms carried out by various emperors throughout the 3rd century? Was it possible to strengthen the military power of Rome during this period, or were all the efforts expended and colossal sacrifices in vain and only temporarily delayed the inevitable fall of the empire?..