De re militari

De re militari
"Concerning Military Matters"
A morocco bound copy of the 1494 edition
Also known as	Epitoma rei militaris, Epitoma institutorum rei militaris
Author(s)	Publius Flavius Vegetius Renatus, though the work was revised a number of times afterwards
Dedicated to	Emperor Valentinian
Language	Late Latin
Date	383 x 450, possibly in the reign of Theodosius I (r. 378-395)
First printed edition	Epithoma rei militaris. Utrecht, 1473.
Genre	military treatise
Subject	military leadership, training, discipline, tactics, logistics, organisation of the army, etc.
Period covered	purports to describe the army in the heydays of the Roman Empire
Sources	include Cato the Elder, Cornelius Celsus, Frontinus, Paternus, Imperial Constitutions of Augustus, Trajan, Hadrian

De re militari (Latin "Concerning Military Matters"), also Epitoma rei militaris, is a treatise by the Late Latin writer Publius Flavius Vegetius Renatus about Roman warfare and military principles as a presentation of the methods and practices in use during the height of the Roman Empire and responsible for its power. The extant text dates to the 5th century AD.

Vegetius emphasized things such as training of soldiers as a disciplined force, orderly strategy, maintenance of supply lines and logistics, quality leadership and use of tactics and even deceit to ensure advantage over the opposition. He was concerned about selection of good soldiers and recommended hard training of at least four months before the soldier was accepted into the ranks. The leader of the army (dux) had to take care of the men under his command and keep himself informed about the movements of the enemy to gain advantage in the battle.

De re militari became a military guide in the Middle Ages. Even after the introduction of gunpowder to Europe, the work was carried by general officers and their staffs as a field guide to methods. Friends and subordinates customarily presented embellished copies as gifts to leaders. It went on into the 18th and 19th centuries as a source of policy and strategy to the major states of Europe. In that sense, De re militari is a projection of Roman civilization into modern times and a continuation of its influence on its cultural descendants.