Vegetius

Publius Flavius Vegetius Renatus wrote when the empire was strained but unbroken, probably in the 380s–390s. His personal life is largely opaque: likely a court functionary with access to archives and an eye for administrative levers. What we have is purpose and posture—he dedicates his Epitoma to an emperor (perhaps Theodosius I or Honorius) and adopts the tone of a reformer calling a great machine back to first principles. He mined older authorities—Cato, Frontinus, Paternus—and recast them for an age that needed clarity.

Vegetius is the key witness for late imperial artillery doctrine. He records that legions maintained artifices—skilled craftsmen—and fabricae to fabricate and repair engines, ensuring that machines could be built to pattern when campaigns demanded them. He specifies that onagers were cart-borne at the cohort level, giving each battalion its own heavy thrower and crew. He notes that artillery deployed behind the heavy infantry line, firing over friendly ranks to break formations and interdict walls, while trained ballistarii served as specialists. These details, preserved in the compact cadence of a manual, show how Rome simplified its arsenal: the onager’s single torsion skein and stout frame replaced the finicky twin-bundle torsion machines as the workhorse of both siege and field support.

Critics then and now have called Vegetius an armchair general, and he invites the charge: he writes from books, not bivouacs. Yet his character reads as practical and moral, not merely pedantic. He rails against the decay of training, insists on drill, and prizes logistics and fabrication. He cares about weapons because they are habits made wood and sinew: machines, like soldiers, must be standardized and reliable. His clarity and insistence on fundamentals—sharp tools, steady formations, rehearsed crews—render him the right man for a collapsing century.

Vegetius’s influence was profound and long-lived. Medieval commanders read him as gospel, and through them his late Roman arsenal echoed far beyond his lifetime. Within this timeline, he is the capstone of a process that began with sapping at Veii and accelerated under Caesar and Trajan. Where Vitruvius gave the math for torsion, Vegetius provides the table of organization: who builds, who hauls, who fires, and where they stand. His pages make plain why late antiquity preferred onagers—they were simpler to keep in the line, easier to cart, and deadly enough to make walls answerable. He closes the Roman story of artillery with a doctrine a legion could carry.