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CHAPTER XVIII. 
OF THE PREPARATION OF THE BALISTAE AND 
CATAPULTAE. 
BEAMs of considerable length must be procured, upon 
which are fixed cheeks in which the axles are retained; 
in the middle of those beams holes are made, into which are 
received the capitals of the catapultæe, well tightened with 
wedges, so that the strain will not move them. Then 
brazen stocks are fixed for the reception of the capitals, 
in which are the small iron pins which the Greeks call 
eriogides. The ends of the ropes pass through the holes 
of the capitals, and brought through on the other side, 
they are then passed round the axle of the windlass, which 
is turned by the aid of levers, till the ropes, both drawn 
tight, give the same tone when struck by the hand. Then 
they are confined at the holes with wedges, to prevent 
their slipping. Being passed through to the other side, 
they are in a similar way tightened by the levers and 
axles till the tones are similar. Thus by the use of the 
wedges, catapultæ are adjusted, according to the effect 
of musical tones on the ear.