Building An Ancient Roman Catapult: A Step-By-Step Guide

Roman catapults were used in ancient times to hurl various objects at enemies during war. The Romans, for example, threw bags of bees at their opponents. Today, catapults are used for entertainment and educational purposes. Building a Roman catapult can be a fun DIY project, and the process involves gathering the right materials, such as wood, screws, rubber bands, and rope, and assembling them according to instructions or personal creativity. Safety precautions must be considered when building and operating catapults to ensure a fun and harmless experience.

Choosing materials: softwood, rope, nails, screws, etc

The materials you choose for your Roman catapult are important, as they will determine the strength and durability of your weapon. Here is a detailed guide to help you select the best materials for the job:

Softwood:

Softwood is an excellent choice for the frame of your catapult. Cedar is a good option as it weathers well and looks authentic, but any type of softwood will do. Make sure you select good-quality timber that is free of knots and splinters, as these can weaken the structure. You will need enough softwood to build a sturdy frame with upright pieces, angled support pieces, and crosspieces.

Rope:

Rope is essential for creating the power behind your catapult's arm. The Romans used linen and horsehair rope, but you can also use natural fibres such as hemp or sisal, which stretch less than nylon rope. You will need a significant amount of rope to create a strong spring by looping it back and forth through the frame.

Nails and screws:

Nails and screws are necessary for connecting the various pieces of your catapult's frame. Use 3-inch lag bolts to connect the frame to the crosspieces, with at least two screws for each connection. For attaching the angled support pieces to the upright pieces, you will need 4 1/2-inch and 5-inch lag screws. A 2-inch finish nail can be pounded into the centre of the throwing arm.

Other materials:

In addition to the main structural components, you will need some foam padding for the top crosspiece to cushion the impact of the throwing arm. You can also add wheels to your catapult for mobility, such as 5-inch casters, or opt for solid wood blocks. A screw eye and a panic snap (available at hardware stores) are also useful for attaching the projectile and controlling the trigger mechanism.

Building a sturdy frame: using cross-braces to prevent implosion

Building a sturdy frame is essential to ensure the catapult can withstand the immense stress exerted on it when the spring is tightened. Without a pair of cross-braces, the machine could implode.

To build the cross-braces, you will need a 12' four-by-four beam. Cut the beam into two 6' lengths, and stand them upright so they are flush with the inside of the frame. Cut another length of 3' from the same beam and save it for later—this will be your cross-brace.

Once you have assembled the base of the frame, you can connect the 6' four-by-four lengths to the base using lag bolts. Remember to pre-drill the holes for the lag bolts, as you will not be able to get them into the wood otherwise. Use two bolts per post, with one through the side of the base frame and the other through the indented 2x4.

Now, you can install the cross-brace. Clamp the 3' length of the four-by-four to the top of the two posts, with the top of the cross-brace flush with the top of the posts and closer to the shorter side of the base frame. Pre-drill four holes into the cross-brace, two on each side, and start screwing in your lag bolts. You can then finish tightening the bolts and remove the clamp. Drill two 1.5" holes into the cross-brace on both sides—this is where the surgical tubing will go, so make sure the holes are smooth to avoid tearing. Add a ton of padding to the cross-brace to protect the catapult/arm from breaking.

With the cross-braces in place, your Roman catapult will have a sturdy frame that can withstand the forces exerted by the spring, allowing you to safely launch your projectiles.

Creating the spring: using twisted rope for power

The power behind a Roman catapult is its spring, which was made from twisted rope in ancient times. The Romans used natural fibres like linen and horsehair, but you can also use modern materials such as hemp or sisal rope, which stretch less than nylon rope.

To create the spring, you'll need to cut two 15-inch segments from a broomstick to serve as torsion handles. The more twists you put on the rope, the greater the torque and power of your catapult will be. Take your rope and tie it to one of the broomstick handles. Then, thread it through the holes in the base and the arm of the catapult, bringing it back and forth through the frame several times to secure it firmly.

Continue this over-and-under motion, looping the rope around each handle with each pass. This will create a figure-eight shape with multiple twists in the rope. The more twists you add, the more tension and force your catapult will have. Finish lacing by going through the frame holes and around the handles, ensuring the loops stay anchored. Finally, knot the end of the rope securely to one side of the catapult arm.

When fully wound, the twisted rope places immense stress on the structure, so it's crucial to build a solid wooden frame with cross-braces to prevent implosion when the spring is tightened.

Adding wheels: for mobility or opting for solid blocks

The onager, a type of catapult used by the Romans, had wheels at each corner of its base frame. This allowed for easy movement and transportation of the weapon. The onager was used to hurl heavy rocks or masses of stones to smash through walls, ramparts, and turrets.

When building a Roman-style catapult, you can choose to add wheels for mobility or opt for solid blocks instead. Wheels provide the advantage of being able to quickly move the catapult into position or adjust its aim. They also allow for easier transportation, especially over longer distances.

If you decide to add wheels, it is important to consider their size and placement. Smaller wheels may be more manoeuvrable but can struggle on uneven terrain, while larger wheels provide better stability. Placing the wheels at the corners of the base, similar to the onager design, can provide a stable platform and facilitate easier turning.

However, opting for solid blocks instead of wheels can also have benefits. Solid blocks provide a stable and immobile foundation for the catapult, eliminating the risk of unintended movement during operation. This fixed position can improve the accuracy and consistency of the catapult's shots. Additionally, solid blocks can be a simpler and more cost-effective solution, as they do not require additional materials or construction.

Ultimately, the decision to add wheels or opt for solid blocks depends on your specific needs and the intended use of your Roman catapult. If mobility and flexibility are important, wheels are a good choice. However, if stability, accuracy, and simplicity are your priorities, solid blocks may be the better option.

Testing: flinging objects like baseballs, not beer cans

Testing your catapult is an important step in the building process. It is a chance to see how far and how accurately your catapult can fling objects. While you may be tempted to try launching beer cans, this is not recommended. Baseballs and burritos, on the other hand, are great choices for ammo.

When testing your catapult, it is important to keep safety in mind. Always stand well clear of the rotational axis of the throwing arm and wear eye protection. It is also important to choose your projectiles wisely. Avoid using objects that could shatter or break, as this could create dangerous flying debris.

To get the most distance out of your catapult, experiment with different lengths of cord attached to your projectile. The longer the cord, the farther your missile will fly. You can also adjust the tension on the spring by twisting the pegs in the direction opposite to the flight of the projectile. However, be careful not to over-tighten, as this could cause the pegs or frame to break.

When releasing the throwing arm, a good trigger mechanism is essential. A panic snap, available at hardware stores, makes an excellent trigger. It is easy to attach and disconnect, and allows for fast, controllable releases. Without a good trigger, you may find that your projectile shoots straight up or plows into the ground in front of you.

By following these tips and tricks, you'll be flinging objects like a pro in no time. Just remember to always put safety first and have fun with your new Roman catapult!

Frequently asked questions