The theme of the book is the history of the Roman Empire during the Antonine and Severan dynasties from the beginning of the reign of the philosopher-emperor Marcus Aurelius to the death of the usurping emperor Marcus Opellius Macrinus, with an emphasis on its military aspect, which is still poorly known to the reader interested in history. Why did we choose this particular period? In our opinion, this was the time of Rome’s last serious attempt to maintain its unconditional dominance in the then ecumene and, at the same time, the last attempt to preserve the ancient civilization of the Mediterranean as a whole, as a cultural and political phenomenon. Before that, Rome did not have such a need, since there were no doubts about its dominance and civilizational progress. Now such doubts have arisen. Rome was subjected to large-scale military attacks, which it could hardly withstand, and the cultural level of the Empire began to decline, although, at first, not very noticeably for its inhabitants. At the same time, a crisis of worldview began to mature, primarily a religious one. Ancient religions, which previously contributed to the development of society, now evoked less and less respect and sincere faith. Fewer and fewer people believed in the ancient gods, with their purely human characters. Accordingly, the moral principles and level of culture of society were questioned and melted. The ruling circles of the empire, starting with Marcus Aurelius and his circle of like-minded people, tried by military force to stop the onslaught of the barbarians, preserve the principles of ancient valor, and breathe new life into the dying faith, morals and customs, but their attempts were in vain. The demoralization of the population, the moral breakdowns of the emperors, the disintegration of the Roman guard and army, the impotence and conformism of the Senate only emphasized this. Still, the Romans were a warrior people, so the purely military and organizational efforts of the Empire gave the best results in trying to stop the decline. It is these efforts that we want to show in this work.