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.

3

---

 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

4

---