A Late-6th Century description of Traction Trebuchets by John, Archbishop of Thessaloniki
The Byzantine historian Theophylactus Simocatta wrote that the Avar
people learned about siege engines from a captured Byzantine soldier -
and then used the machines on their teacher's cities.
Theophylactus names this Byzantine as Bousas and says that he, in
exchange for his life, constructed for the Avars a siege engine called
a "helepolis" or "City Taker" (a heavy trestle-framed traction
trebuchet).
In 587 the Avars, using this new technology, besieged and took the
fortress of Appiareia in what is now northern Bulgaria. Here is part of
Theophylactus' account:
"Bousas
taught the Avars to construct a certain siege machine, for they [the
Avars] happened to be most ignorant of such machines, and he built the
helepolis to hurl missiles. Soon thereafter the fortress was leveled,
and Bousas collected judgment for their inhumanity, having taught the
barbarians something frightful, the technology of besieging. Thence the
enemy captured effortlessly a great many of the Roman cities by making
use of this original device."
Ten years later, in 597, the Byzantine centre of Thessaloniki was
besieged by Avaro-Slavic forces. The attacking army didn't fool around
- they attacked with fifty large traction trebuchets that could hurl
"great stones" into the town. In his description of the siege John,
Archbishop of Thessaloniki, calls the big traction trebuchets
"petroboles" (Greek for "rock thrower"). Smaller machines were called
"lithoboles" or "stone throwers".
"These
petroboles were tetragonal and rested on broader bases, tapering to
narrower extremities. Attached to them were thick cylinders well clad
in iron at the ends, and there were nailed to them timbers like beams
from a large house.
These timbers had the slings from the back side and from the front
strong ropes, by which, pulling down and releasing the sling, they
propel the stones up high and with a great noise. And on being fired
they sent up many great stones so that neither earth nor human
constructions could bear the impacts.
They also covered those tetragonal petroboles with boards on
three sides only, so that those inside firing them might not be wounded
with arrows from those on the walls. And since one of these, with its
boards, was burned to a char by a flaming arrow, they returned,
carrying away the machines.
On the following day they again brought up these petroboles covered
with freshly skinned hides and with the boards, and placing them closer
to the walls, shooting, they hurled mountains and hills against us. For
what else might one term these immensely large stones?"
Rough notes:
We are somewhat at the mercy of the
translator here (or at least, I am, having no knowledge of Greek nor
access to the original document..). This is the best I can manage for
now:
Cylinders:
I can only assume that this refers to the axles of the
machines as these cylinders rest on the machines' bases and have the
throwing arms attach to them. The comment about "well clad in iron at
the ends" is interesting. Following along on the axle idea, this may
refer to a bearing surface (either on the axle or the stationary frame
timbers) or to a re-enforcement driven onto the end of the axle timber
(perhaps to stop it splitting).
Tetragonal:
Basically, the machines are described as having bases that
resemble a pyramid with its top removed, as in the illustration I have
used on this page - although it is possible that the front and rear
faces could be rectangular, with only the sides tapering. I have seen
this interpretation in a few modern drawings.
Oddly enough, this page's illustration hints at an arrangement the other way around - with rectangular faces on the sides.
Loud Noise:
This is a bit of a puzzle to a modern reader. The noises made
by a "Frankish" traction trebuchet (where the beam can swing unimpeded
between the supporting timbers) are generally just the creak of flexing
timbers and axle bearings, a whip-like crack from the suddenly unfurled
sling and the buzz of the rapidly spinning projectile through the air.
Unless we assume that 6th Century ears were enormously more delicate
than our own noise-shattered ones, we are left to contemplate what else
this loud noise was. - One possibility is that the crew was making the noise,
possibly chanting to keep time and bellowing during the strenuous pull.
On the other hand, you might expect this to be described as a loud cry
or shout. - Another more likely possibility is that the base of the beam
struck the frame. Many machines illustrated on the Grey Co Trebuchet
page seem to be drawn as if they do this. This practice would work,
although at the cost of shorter machine life as the trebuchet hammered
away at itself. On the other hand, in these machines the crew is
standing behind the protective front framework, so anything that would
catch the beam end would also be in the way of the pulling crew's ropes. - Finally, the noise may refer not to the flight of the
projectile but to its impact (although the text as it stands here
doesn't seem to support this one)
Great Stones:
"so that neither earth nor human constructions could bear the
impacts".. Generally, the traction trebuchet is considered to be a
relatively light weapon, throwing stones of a only few (say, 10) kilos
in weight - making it more an anti-personnel weapon able to destroy
only light structures. Either John's comments are in awe of the new
weapon (he felt the need to describe what one looks like), contain wild
exaggeration or, just possibly, are an accurate description (in which
case we would need to revise our ideas on how big traction trebuchets
could be - even very early ones such as these).
Alternatively, if the human construction being discussed here is a
tiled roof, then perhaps it is entirely believable, even on a modest
scale. If you are not looking at massive stonework then even a stone of
a few kilos, flying at perhaps 160 km/hr (100mph) or dropping from a
great height, could do significant injury or damage to civilian-style
buildings.
John describes the throwing arm as being as large as a beam from a
large house. This might give an idea of size - if we learn what is
meant by a "large" house...
Reference
The above quote is taken from "The Traction Trebuchet: A Reconstruction
of an Early Medieval Siege Engine" by W.T.S. Tarver's who, in his
footnotes, credits the source and translation as
'Chevedden, "Artillery Revolution", after Speros Veryonis jr "The
Evolution of Slavic Society and the Slavic Invasions in Greece: The
First Major Slavic Attack on Thessaloniki, AD 597", Hesperia 50.'
and
"The Invention of the Counterweight Trebuchet: A Study in Cultural Diffusion" by Paul E. Chevedden
Tarver notes that Chevedden uses the original word "petrobole" (ie
"rock thrower") rather than Veryonis' translation to "ballistrae", with
its implications of torsion power.
