Nunc vero quae ad praesidia periculi et necessita-tem salutis sunt inventa, id est scorpionum et ballistarum rationes, quibus symmetriis comparari possint, exponam.
We now turn to the inventions which serve both to protect against danger and to satisfy the needs of safety; I will set forth the construction of scorpions and balistae with the proportions on which they are based.
final_alignments\Vitruvius_Architecture_Book_10.json