TOM #15


 In 1271 when Marco Polo left Venice at the start of his journey to the land of the Kublai Khan, there was another Marco that traveled with the expedition.


The only positive thing one can say about warfare, is the rapid advance and improvement in technology during hostilities, provided these innovations are passed on to peace-time engineering.

Researching Mongol history for my book, The Other Marco, I came across the siege of Xiangyang, a huge fortressed city in southern China.  History tells us that the Genghis Khan conquered northern China and his grandson Kublai Khan eventually overran the southern Song dynasty.  One of the hardest nuts to crack was the massive walls of Xiangyang.  Kublai Khan therefore acquired the expertise of two Persians, Ismail and Al al-Din to build rock hurling siege machines to break this barrier.  These engineers improved on an older design and surrounded the city with 20 of these new weapons that could toss a projectile of 300 kg from a distance of 500 meters.  The strongest fortress in southern China fell quickly, which opened the door to the rest of the country, thanks to this new technology.

Let’s have a look at these rock-lobbing monsters.

Machines that flung projectiles [mostly rocks] appeared hundreds of years earlier in China itself and during Roman times.  These prototypes were possibly more dangerous to the soldiers loading and firing them than for the enemy.  During the middle ages there seemed to be a resurgence of siege weapons, perhaps because more castles were being built at the time.  Needless to say, the more siege machines being built the quicker new ideas improved the design.

I will not dwell on the older machines but will look at the Mangonel firstly as the fore runner of the Trebuchet.


All siege machines have a heavy wooden framework to contain the arm that flings the projectile.  This arm is powered in three different ways, tension, torsion or gravity.  Earlier Mangonels [or Onager] used the ‘tension’ method.  Bending a thin piece of wood with one’s hands [putting it under tension] and then flicking a small pebble from the open end is how it worked, only much bigger, of course.

The piece of wood is in tension

Another version of the older Mangonels was to have a huge crossbow adding to the tension by attaching the bow string to the launching arm so that when this arm was loaded [bent back] the crossbow was loaded at the same time [adding more tension].  In spite of doubling the power, it was not always strong enough to breach castle walls.  This called for a new method for storing energy that the launching arm could harness. It was eventually found by twisting ropes and sinews around the base of the arm to form a torsion bundle.

Torsion [twisting] builds energy in the winding.




Notice the twisted cordage at the bottom of the launching arm and the slotted wheels on either side that are used to tighten the bundle by inserting poles into the slots and turning.  There is also a pin jutting out that must be inserted into one of the four ‘braking’ holes on the side of the wheel to stop the twisting unravelling itself before the rock is thrown.  This is a very simplified drawing of a working Mangonel as I have not shown the complex tackle used to lower the arm back down to the firing position, nor have I shown the trigger method for holding down the load and letting go when the command to “Fire!” is given.  No single man could hang onto the rope as I have drawn – I am simply having a bit of fun!

Mangonels were not very energy efficient, as too much of the stored energy in the twisted bundle is used directly in moving and lifting the weight of the launching arm.  The projectile uses whatever energy is left to break the wall.  Another drawback of the Mangonel’s launching system is that the arm has to be stopped at full speed against a padded framework which surely damages not only the contact areas, but the whole structure through continual vibration.  I wonder how long the average Mangonel lasted before being rebuilt.

Some machines had wooden wheels but would be more stable without them during operation.




The design of the Trebuchet is quite ingenious.  It also has a launching arm to fling the projectile by means of a falling counter-weight to produce the required energy through gravity.  The launching arm is pivoted to one side where the hinged weight is attached.  This causes the end of the long side to move through a greater arc increasing it’s velocity.  A sling holding the projectile is attached to this fast moving end.  Because the sling is free moving, it swings out through centrifugal force to its full length, scribing an even greater and faster moving arc that flies high over the machine.  At this point, a simple angled pin allows the one side of the sling to slip off and free the payload to fly at, or most times over the walls and into the castle.


It was this release mechanism that intrigued me most, and that is why I have drawn it here.  It is so simple and yet so brilliant!  [Again I have not included in the illustration, any of the ropes used to retrieve the arm or lift the weighted bucket, neither the holding down trigger mechanism as I felt it would complicate the picture unnecessarily.]  Let us not forget how the power was increased through velocity by moving the business end out as far from the pivotal point as possible. This is nothing short of sheer brilliance as well.  Small wonder the fortresses of the southern Song dynasty crumbled before the invading Mongols.

Siege machines were eventually superseded by gunpowder and canons.  The only ones still found today are scaled down models built by enthusiasts who compete against each other at staged competitions.  Sounds like fun!


In the book, The Other Marco, TOM travels from Venice with its Grande Canal to China’s Grande Canal with its system of locks.  TOM is intrigued by this innovation, so, perhaps we could have a look at locks and how they work in the next posting which will be TOM #16.  Being an even numbered edition it will of course include the Monsters 4 Monsters section.  We will have to incubate and deliver a monster by then.  See you there.