PART I INTRODUCTORY NOTES ON ANCIENT PROJECTILE ENGINES
OF ancient Greek authors who have left us accounts of these engines, Heron (284- 221 B.C.) and Philo (about 200 B.C.) are the most trustworthy.
Both these mechanicians give plans and dimensions with an accuracy that enables us to reconstruct the machines, if not with exactitude at any rate with sufficient correctness for practical application.
Though in the books of Athenaeus, Biton, Apollodorus, Diodorus, Procopius, Polybius and Josephus we find incomplete descriptions, these authors, especially Josephus, frequently allude to the effects of the engines in warfare ; and scanty as is the knowledge they impart, it is useful and explanatory when read in conjunction with the writings of Heron and Philo.
Among the Roman historians and military engineers, Vitruvius and Ammianus are the best authorities.
Vitruvius copied his descriptions from the Greek writers, which shows us that the Romans adopted the engines from the Greeks.
Of all the old authors who have described the engines, we have but copies of the original writings. It is therefore natural that we should come across many phrases and drawings which are evidently incorrect, as a result of repeated transcription, and which we know to be at fault though we cannot actually prove them to be so.
With few exceptions, all the authors named simply present us with their own ideas when they are in doubt respecting the mechanical details and performances of the engines they wish to describe.
All such spurious information is, of course, more detrimental than helpful to our elucidation of their construction and capabilities.
It frequently happens that in a medieval picture of one of these machines some important mechanical detail is omitted, or, from the difficulty of portraying it correctly, is purposely concealed by figures of soldiers, an omission that may be supplied by reference to other representations of the same weapon.
FIG 1. -- BESIEGING A FORTIFIED TOWN WITH A BATTERY OF CATAPULTS AND BALLISTAS. Criticism. In this picture the ballistas are fairly correct, but the catapults are too small. From Polybius. Edition 1727