A number of maxims have their origin in Vegetius, the most familiar of which is "He...who desires peace, should prepare for war" (III.Preface). Others are collected in III.26, which, in the Middle Ages, was the most popular part of the Epitome. Indeed, the number of surviving manuscripts rival the Natural History of Pliny. Other sage advice includes the following:
It is the nature of war that what is beneficial to you is detrimental to the enemy and what is of service to him always hurts you.
It is much better to overcome the enemy by famine, surprise or terror than by general actions, for in the latter instance fortune has often a greater share than valor. Those designs are best which the enemy are entirely ignorant of till the moment of execution. Opportunity in war is often more to be depended on than courage.
Valor is superior to numbers.
The nature of the ground is often of more consequence than courage.
Few men are born brave; many become so through care and force of discipline.
Troops are not to be led to battle unless confident of success.
An army unsupplied with grain and other necessary provisions will be vanquished without striking a blow.
Consult with many on proper measures to be taken, but communicate the plans you intend to put in execution to few, and those only of the most assured fidelity; or rather trust no one but yourself.
Punishment, and fear thereof, are necessary to keep soldiers in order in quarters; but in the field they are more influenced by hope and rewards.
Good officers never engage in general actions unless induced by opportunity or obliged by necessity.
Aside from these familiar quotations, there are other, more intriguing, observations. Vegetius, for example, felt that soldiers should be recruited from temperate climates because they have more blood and consequently are less afraid of being wounded (I.2) and that the country dweller is more fit to be a soldier than a recruit from the city, a man fearing death less if he is not acquainted with the luxuries of life (I.3). Recruits also should be tattooed as an official mark of service only after they have demonstrated their fitness to serve, which was a period of four or more months (I.8, II.5). They should be expected to cover twenty miles in five hours or, at a faster step, twenty-four miles; carry a pack weighing approximately 43 pounds; and be able to swim and to vault a horse (I.9, 10, 18, 19). As to the legions, themselves, (so-called because soldiers were "selected"), a fortified camp was expected to be surrounded with a fosse twelve feet wide and nine feet deep, and a revetment another four feet high.
An abridgement of "the instructions and observations of our old historians of military affairs, or those who wrote expressly concerning them" (Preface), it is likely that the Epitoma Rei Militaris was dedicated to the Byzantine emperor Theodosius I, probably in the AD 380s, sometime after the death of Gratian in AD 383. But his plea for courage and discipline and the revitalization of the legion could not save Rome, which would be sacked by Alaric and the Goths within the next two decades.
References: Flavius Vegetius Renatus: The Military Institutions of the Romans (1767/1944) translated by Lieut. John Clark; Vegetius: Epitome of Military Science (1996) translated by N. P. Milner.