At the end of the fourth century AD, the civil servant P. Fl. Vegetius Renatus composed a treatise on the Roman army, Epitoma rei militaris, which is in fact the only extant work of this kind. Throughout the Middle Ages and the Renaissance, Vegetius’ manual was often commented and translated. Essentially, the Epitoma consists of four books. Book 1 deals with the recruit, Book 2 with organization, Book 3 with strategy, and Book 4 with fortifications and naval warfare. The second chapter of Book 3 describes how to manage the health of the army: quemadmodum sanitas gubernetur exercitus.
Vegetius
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Epitoma rei militaris Codex on parchment 12th c. England? William L. Clements Library