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The Chinese Xuan Feng or "Whirlwind"

Until the advent of gunpowder, the trebuchet (French: trébuchet) was a common powerful siege engine that used a long arm to throw a projectile. There are two main types of trebuchets. The first, called a mangonel throughout mediæval Europe, is the traction trebuchet that uses manpower to swing the arm. This type first appeared in China before being carried westward by the Avars. The technology was adopted by the Byzantines (the eastern Roman Empire) in the late 6th-century AD and by their neighbours in the following centuries.

The later, and often larger, counterweight trebuchet[1] uses, as the name implies, a counterweight to swing the arm. The counterweight is typically a box structure filled with earth or stones attached to a pivot at one end of the arm. By elevating the box and then allowing it to fall imparts kinetic energy to the arm that rotates about a fulcrum and projects a missile in much the same way as a staff sling. The counterweight trebuchet appeared in both Christian and Muslim lands around the Mediterranean in the 12th-century, returning to China via the Mongol conquests in the 13th-century[2].

Traction Trebuchets As mentioned above, the earliest type was the traction trebuchet, developed first in China by the 5th- or 4th-century BC. Probably used by the Mohists, descriptions of it can be found in the Mojing compiled in the 4th-century BC. The trebuchet consisted of an arm and sling mounted on a wooden frame, sometimes with wheels. Those mounted on wheels were said to have needed 200 men to manoeuvre each of them[3]. To operate the trebuchet, a team of men pulled on ropes attached to the end of the shorter segment of a long wooden beam that rotated round an axle fixed to a base framework. In so doing, the longer segment of the beam was propelled in a forward arc until its sling released a missile.

As defensive weapons, traction trebuchets were positioned behind city walls and guided by an "artillery observer" on the walls. Range was determined by the strength and number of men pulling. Increasing and decreasing range meant adding and removing men from the pulling ropes[3]. In Chapter 14 of the Mojing, the traction trebuchet is described hurling hollowed out logs filled with burning charcoal at enemy troops[4].

The “Whirlwind” "Four footed" and Xuànfēngpào (旋风炮), or "Whirlwind", trebuchets appeared during the Tang dynasty[3]. Essentially the same as previous weapons, the design of the four footed trebuchet offered good stability and thus these weapons could be made much larger. By contrast, much emphasis is made of the Whirlwind's smaller size and lighter weight to aid transportation. All of which reminded me of a Discovery Channel episode of the Ancient Discoveries series that looked at Chinese warfare[5]. If remembered correctly, then mention was made of the Whirlwind and its capabilities.

In the early 2000's China was becoming much more open to the West and in particular western scholars. Consequently, there were a spate of documentaries revealing hitherto little known Chinese innovations to a wider audience. Sadly, such programmes gave the impression that the Chinese were technically superior to western societies in pretty much all respects. This point of view is often expounded today and, frustratingly, it ignores the rich history, wisdom and technological advances made around the Mediterranean.

The Whirlwind is an example of this imbalance. The documentary described this traction trebuchet's operation, including its 360 degree rotational ability, and revealed it could propel a missile 150 yards. Wait, what? Did I hear that right, one hundred and fifty yards? That is just a little over 137 metres and, if correct, means the Whirlwind would have to be positioned well within contemporary bowshot[6] of its intended target. The several operators needed to pull the ropes to launch a missile would be extremely vulnerable to arrows. Presumably the Chinese would have used some form of defensive breastwork or shield-like structure, but this still does not detract from the weapon's poor performance. As a comparison, in the 4th-century BC the ancient Greeks were deploying weapons like the gastraphetes ("belly bow") and even more powerful torsion catapults that could easily shoot more than double the Whirlwind's vaunted range.

Descriptions are seemingly based on images such as that shown right. Accordingly the basic Whirlwind described as using a single vertical pole mounted on a base with two legs, which would be driven into the ground to provide stability[7]. Confusingly, the same anonymous source then states it could be rotated 360° for an exceptional field of fire. Presumably the weapon had some form of swivel not evident in the image right.

Such contradictions are indicative of an awful lot of bumpf that can be found on the web. Descriptions of the Whirlwind are frequently repetitive as if drawing on a single source and most are unreferenced. In other words there are a lot of claims made that are difficult to corroborate.

As one example, according to Nixon (2015): "like a sniper rifle, the whirlwind catapult was a one-shot, one-kill form of attack."[8] If you want corroboration of the weapon's accuracy, then go no further than McBride (2015): "This catapult was generally used like the sniper version of a rifle. It wasn't the power of the punch that mattered, but the accuracy of the shot."[9] These two "sources" seemingly provide corroborating evidence for the Whirlwind's sniper-like accuracy. Except, of course, that neither on-line author cites any references to support their claims. What we are left with could be the author's fiction, simple supposition or more likely a form of hearsay as it is suspected that both sources are drawing on each other creating circular reporting. And this is the real crux of the issue. Given the evidence as presented, the Whirlwind does not seem the wonder weapon. It would be useful if better, referenced material could be provided to evaluate this ancient weapon more objectively, but perhaps it does not exist.


1. Also known as the counterpoise trebuchet.

2. By the 9th-century a hybrid of the traction and counterweight trebuchet, employing manpower and a pivoting weight, was used in the Middle East, Mediterranean Basin, and Northern Europe. By the 12th-century, the full-fledged counterweight trebuchet was developed under the Ayyubid dynasty of Islamic Syria and Egypt (described by Mardi bin Ali al-Tarsusi) and used in the Third Crusade. By the 13th-century, the counterweight trebuchet found its way into Song Dynasty (960 to 1279) China via the Mongol invaders under Kublai Khan (r. 1260 to 1294) who used it in the Siege of Xiangyang (1267 to 1273).

3. Turnbull, S. (2001), Siege Weapons of the Far East (1) AD 612-1300, Osprey Publishing.

4. Liang, J. (2006), Chinese Siege Warfare: Mechanical Artillery & Siege Weapons of Antiquity, Leong Kit Meng, Singapore.

5. Discovery Channel (2007), Ancient Discoveries, Series 3, Episode 7 "Chinese Warfare", originally aired March 6th, 2007.

6. The author has shot a 50 lbs draw weight recurve bow further than 150 yards. Warbows were of much greater power.

7. Arms & Armor of the Three Kingdoms, Anonymous Tumblr account, retrieved July 17th, 2020.

8. Nixon, E. (2015), “10 Insane Ancient Weapons You’ve Never Heard Of”, Listverse, retrieved July 17th, 2020.

9. McBride, G. (2015), “What was Siege Warfare in China like around the year 1BCE?”, Quora, retrieved July 17th, 2020. Interestingly, George McBride, who “knows about History” according to their biography, has provided 130 answers on the Quora website but “has not filled out their profile”. Typically the mysterious “George” fails to cite any references for the answer provided.

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