Technology and Features

Historically correct

Our models are to an extent historically correct. That is, we designed them based on the best available sources and we are always seeking to improve them as new archaeology findings and science are made available.
That is especially relevant for our “classical” (roman/greek) models that take into account the proportions and design that came down the centuries on treatises and books of authors such as Vegetius.
So, to that extent one can say “Yes, this would be what a XIIIth century bolt-thrower would be like.” Or “Yes, this is a three-span roman scorpio.”
They were built with modern technology and materials and have features adequate for re-enactment, which are obviously not historically correct. But rest assured that on a close-up inspection, no layman would spot the difference, and at - let’s say a three meter distance - no history buff would spot it, too.
In each model’s page we detail to what extend the machines deviate from the historicity. Please remember that it is done to only to provide with a better service to our clients. As options, we offer variations of our models that increase their “historical correctness”, but with drawbacks in performance, security and cost.

Life Size

Our models are not small-scale toys; they are the real thing, measured in meters and kilograms. You could take them and put them on a castle wall and defend it against invading hordes.
Although the weight depends on the model and choice of size, the whole set it will still be more than 75 kg and it will occupy at least 5 square meters.

Authentic look

Although we use modern materials and techniques (e.g. composite construction, machine tools) to build our engines, those features are cleverly disguised. One needs to look very, very closely (and it most cases, disassemble some parts) to find the tell-tale signs of modern-building.
Our medieval models bore a heavy rugged look and they play the part in any medieval fair and our aim is that our roman ballistae would not be out of place as a replica in an Archaeological museum.
We claim that they are just beautiful.


Our engines are more than pretty faces, they work well too. Our standard models are designed to pull a “paltry” 300 kg/750 lbs of strength, that we figured that is more than enough for any re-enactment purpose (its intended use).
Having said that, it is clear that our engines are not toys, they are artillery, which is a form of weapon. Our ballistas can sent a bolt flying 200 meters to pierce a 1 cm wood board.
The dangers of operating it are similar to any other archery event (bow, crossbow). It includes security measures like not pointing at persons, animals and other people’s property, check lines-of-fire, check blind lines-of-fire, detail spotters, limit spectator access and have insurance.



Years of experience in re-enactment taught us the need for equipment that is easy to transport and quick to deploy. We figure that it is an important feature which our clients would appreciate, from professional reenactors to “weekend warriors”.

So we designed the standard models of our machines to be easy disassembled in parts that one person can carry, and for the whole machine to fit in a basic estate / MPV car (at least 1550 litres of trunk space with the folded seats). On the left we can see 2 (two!!) balistas loaded on the trunk of an MPV with enough space for all other medieval gear one can need such as armor weapons and clothes.

As an option there is a scaled up versions of the same machines sized up for a Group F van (Ford Transit like, with 6 square meters of area / 2,5 meter long of space).


Safety starts with reliable equipment, that won’t break or malfunction. The machines were design with security margins between 200% and 3000% between the theoretical breaking strains and the loads and forces for which they were design to withstand.

Computer models


We plan and work in Computer Aided Design (CAD) tools, both 2D and 3D. Besides the obvious blueprinting usefulness, it that allows to run simulation models that predict machine performance, component behaviour and breaking strains. And we like it.



Example: One of the composite arms with the work load of 1500N (+/- 150Kgs)

Empirical testing


We also field-tested the machines applying with double of the forces and we determined the real breaking strain of some components through series of destructive test.: we broke a lot of balistas arms, so that yours don't.





Composite construction


Composite construction is used for strength and safety and to prevent warping. Great care was taken to disguise these modern features. For example, all wood parts are reinforced with invisible metal joints and parts. No screws or modern DYU parts are visible.


Example: Assembly of the side panel with the central beam holder ( 10mm support pins fixed in place with epoxy. Maximum work Shear Stress 5MPa - Shear resistance 230MPa)


Cerco21’s Work Concept

We Research > We Project > We Build > We Test > We Shoot !!! > and only then we make it available to costumers, so that they get proven technology.
So we have models on project phase and new models are coming up regularly (so visit our web page often).
Our work concept also allows us to easily accommodate any special requests, in design or size.


Technology & precision

We use machine-tools and technology like laser cut and water jet cut, that allow us to obtain 0,2 mm tolerance for all metal parts and 1 mm tolerance for wood parts. From design to build phases, we use hard-engineering approach to produce precision equipment. We’re engineers and we just can’t help ourselves to avoid it.





Continuous improvement

We strive to keep the pace of recent archaeological and historical findings so that we can build increasingly accurate models. We also are always on the look for better construction technology and different composite materials.


Spares and support

Not only each machine comes with a comprehensive manual (detailing assembly, operation, disassembly and maintenance), but we also provide full technical support.
Good and sturdy as our machines may be, wear and tear takes its toll. In the event you loose, misplace or damage a component and have the need to replace it quickly, rest assured that we can provided you with a full stock of spares.




Besides choices in size, we offer as options choices of woods (oak, pine), finishes (varnish, wax) or decoration (piro-engraving of coat of arms in your medieval ballista or a cremona-type battle shield for your scorpio).  Check the available options in each model’s page.
We can build any new machine that you wish (and would love to) or adapt and adjust our existing models to your satisfaction (size and Force). Just contact us.