1 The Birth of Science - MSRI

94 4. Scientific Technology
to the siege of Perinthus by Phillip II of Macedonia, in 340 B.C., while torsion
catapults able to throw stones were probably first used by Alexander,
during the siege of Tyrus in 332 B.C. The power of these weapons grew
rapidly during the third century. 40
Missiles of a range of weights could be thrown by the different machines.
We have found in various arsenals shot ranging from 10 minae
(4.4 kg) to 150 minae (66 kg). 41 As to their reach, specialists disagree: some
believe it was under 200 meters, whereas others think it may have exceeded
300 meters. 42
The effectiveness of Hellenistic catapults is proved by the fact that fortification
techniques changed following their introduction. 43 (Much the
same happened after the introduction of firearms.) Progress in artillery,
however, left behind advances in defense, as seems to be demonstrated
by a rapidly increasing number of victorious sieges. 44 There is an obvious
correlation between the increasing difficulty in defending the perimeter of
a city and the development of the great Hellenistic states.
One salient novelty of Hellenistic military technology was that the new
weapons were not the fruit of the ingenuity of individual artisans or generals,
but were designed with the participation of the greatest scientists of
the time.
In torsion catapults elastic energy was stored in bundles of animal fibers
(sinews or hair), but the third century B.C. also saw experimentation with
weapons based on alternative elastic materials whose properties were then
being investigated. Thus Ctesibius designed and built artillery weapons
based on metal alloy springs and others based on air springs. The latter
were similar in structure to torsion catapults (see Figure ??), but propulsion
was effected by air compressed inside two metal cylinders by means
of pistons. Contact surfaces were treated for airtightness, so when the
launching arm was pulled back, pushing the pistons in, such high pressures
could be achieved that upon release the stone shot would be hurled
“a very respectable distance”. According to Philo of Byzantium, to whom
40
The main source for the rapid technological development of artillery weapons in the first half
of the third century B.C. is Heron’s Belopoeica (which is included in [Marsden: TT]), based on a
homonymous book by Ctesibius.
41
See [Marsden: HD], pp. 81–83. Much heavier stone balls have been found, but it is thought that
they were meant not to be thrown but to roll down the walls onto the enemy’s siege train.
42
McNicoll discusses all the available data, reaching the conclusion that ranges between 350 and
400 meters could be achieved ([McNicoll], p. 5).
43
See [Winter], [Marsden: HD], pp. 116–163, and [McNicoll]. Fortified walls not only became
thicker and started being surrounded by moats, but were complemented by towers capable of
hosting catapults.
44
A table showing a sharp drop in the number of cases of successful resistance between 322 and
303 B.C. is given in [McNicoll], p. 47.
Revision: 1.14 Date: 2002/10/24 04:25:47