Torsion-Powered Engine; "Qaws ziyar" by al Tarsusi

The frame of this equipment is unseasoned oak, put together with
half-butt joints, and large iron nails.  Each piece of wood used in
the construction of this weapon was approximately one span (20 cm)
square while the vertical timber at the front of the weapon
was two spans across with bronze plates around both sides
of an arch shaped hole through which the arrow / dart was shot.
Twisted skiens of horsehair and silk were looped around the frame.
In the above drawing the bowstring has been pulled back into a slot
cut into a groove across the top of the horizontal stock.  The oak
trigger pushed up a pin releasing the bowstring.

Redrawn and Enhanced  by Marcus Audens.

Reference; D. Nicolle, "Medieval Siege Weapons (2)." Osprey, 2003, N.V. 69  

Shabakah - 4

Shabakah -3, Back Side

The rear panels of heavy cloth and raw wool has been removed to provide a view of
the rope net  under the over- layers 

Shabakah 2 - End View

Shabakah 1

The above is a screen which was used to protect siege workers from
darts and arrows launched from special catapult siege machines.
 It was designed to stop and hold such missiles.

Da Vinci Catapult, End View - 2

Da Vinci Catapult, End View