Flavius Vegetius Renatus, commonly known as Vegetius, was a Roman writer and military theorist of the late 4th and early 5th centuries. His full biographical details remain obscure, with the absence of substantial contemporaneous records; however, he is best remembered for his treatise 'De re militari' ('Concerning Military Matters'), an influential work on Roman military principles and practices. Comprising a preface and four books, it touches on topics such as military recruitment, training, equipment, and tactics. Vegetius aimed to preserve ancient Roman military methods, at a time when the Western Roman Empire was facing internal decay and frequent barbarian invasions. His advocacy for a return to the traditional Roman legionary system and his adage 'Si vis pacem, para bellum' ('If you want peace, prepare for war') have left a lasting impression on military thinking. Vegetius' 'De re militari' became a standard military manual throughout the Middle Ages and into the Renaissance, studied by commanders and scholars alike. His work influenced the revival of classical military ideas and was used as a reference as late as the 18th century. Vegetius' literary style is didactic, aiming to instruct rather than entertain, and characterized by a nostalgic respect for Rome's imperial past. Even with scant details about his own military experience, Vegetius' contributions have made him a seminal figure in the annals of military literature.