The images of bolt-shooters on the Trajan’s Column document a change in the conception of Roman torsions artillery.  During the 3rd century B. C. these weapon systems were in use in the Roman army. The arrow-catapults were constructed in a traditional, Hellenistic style. The torsion-springs were installed in a short distance from each other and the spring-frames consisted of wood with iron or bronze plating.

On Trajan’s Column, which was erected in 113 A.D., another type of arrow-firers in an absolutly different kind of spring-frame construction is depicted.

The distance between the  torsion springs is clearly bigger, the spring-frames are made of iron and the torsion ropes were covered with sheet metal capsules to protect them against external influences. 

Unfortunately there are no discoveries of bolt-shooter parts that correlate with the Trajan-catapults. Discoveries of weapon parts in Gornea and Orsova (Romania) come from late ancient fortresses of the 4th. century A.D., but regarding their design, the construction corresponded to the weapons on Trajan’s Column. 

The torsion systems are also mounted at a great distance from each other and there is a characteristic arch out of wrought iron, which resembles the workmanship on  Trajan’s Column. 

The great distance of the torsion-springs only allows one reasonable conclusion: These bolt-shooters are equipped with internal catapult systems. 

Another discovery in the Mesopotamian town Hatra (dated at the middle of the 3-rd. century A.D.)  constitutes an additional indication of an internal-catapult system: the spring-frame was made of wood and was plated with bronze fittings, but the torsion-springs were arranged nearly 2m apart. The spring- frame was fitted with half round storage points faced inwards for the catapult-arms. This construction  only makes sense for an internal catapult system, because the arms rested in these shapes when not beeing stretched.

In 2003 Dr. Michael Lewis published a paper in „World of Archaeology“ dealing with internal catapult- systems. He had noticed, that the previous reconstructions of  bolt-shooters from the Late Classic Period (Orsova, Hatra) with outwards functioning catapult arms showed inconsistencies. After the conversion to an inwards functioning catapult system, it became a useful bolt thrower.Lewis carried out tests on outwards-swinging and inwards-swing bolt-shooter models, with the resultn that the increase in performance of externally functioning machines for swinging catapult systems was more than 50%.

The idea of internal catapult systems was not new. In the second half of the 19th. century the French scientist Victor Prou reconstructed a stone-projector (palintonon) with an internal catapult system.

The representations on Trajan's Column with torsion systems at a great distance suggest that inwards swinging arm systems were in use.

On Trajan's Column both wars of the emperor against the Dakien (modern-day Romania) - which
took place between 101 and 105 A.C. - are propagandistically depcted.  Because these weapons      
were operational, the development must have taken place in the last quarter of the 1 st century.        

It' unknown who developed these new weapon systems is unknown. Apollodorus from Damaskus,
an ingenious architect, technician and moreover a friend of the emperor is perhaps a possibility.                                

In that case it cannot be ruled out, that the emperor himself - who was in addition to his administrative abilities, a formidable military officer – exerted influence on this development. Under the reign of Trajan the empire was at the zenith of its power. Besides the technical competence (Apollodorus?) the economic and personnel resources for a reconception of the roman torsion artillery also were available.
Finally an authority (Trajan) must als have been necessary to implement such a dramatic change in the innovation of arrow-shooter design against persiting traditional military structures.


Trajan (born 53 A. C. died 117 A.C.
Regency 98-117 A. C.

The representations on Trajan's Column show solidly built and obviously standardized arrow-throwers. The recognisable construction elements make a functionally well proportional impression. The construction appears works „harmonious “.
In the context of this internet site, the illustrations of the Trajan's Column were first submitted for intensive analysis. Then a 3D model reconstruction of the bolt-shooters shown took place withe teh use of a CAD- system. Further the evidence of the significant increase in output of internal catapult systems in relation to conventional systems was generated by a computational simulation. These results coincided with the practical testing of a cannon reconstruction rebuilt intor an internal catapult system. The ancient weapon systems on torsion basis represent a fascinating part of ancient technology, whose origin is dated at the 4th century B. C.. The bolt-shooters of Trajan's Cloumn were thereby the result of 500 years of development. They were highly developed weapons, which corresponded to the state of the art of their time.

Picture credits: Picture Trajan' Column, Matthias's cable, GNU Free documentation License
Picture Trajan, GNU Free documentation License Further source references: See menu option references