Si vis pacem, para bellum." -Flavius Vegetius Renatus, The Military Institutions of the Romans, (390 A.D.) The Military Institutions of the Romans (original title in Latin De re militari) is a treatise by Vegetius, a 4th century Roman writer about Roman warfare and military principles. This treatise taught the lessons of the Ancient Roman way of war to the political and military leadership of the 4th century.During the following centuries, The Military Institutions of the Romans became the most influential military guide for military leaders and officers throughout Europe from the Middle Ages into the 18th and 19th centuries. Even today, it is a valued source of policy and strategy relevant to modern day Western armies.The current abridged edition, including Books I-III, was translated by Lieutenant John Clarke in 1767.