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I've read that Roman catapult were made out of iron and I was wondering if it was possible to replace that iron with bronze instead. In a world where bronze is readily available, copper and tin..etc are abundant while iron/steel aren't.

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    $\begingroup$ You heard wrong. Roman siege machines were made of wood, not iron. They may have used iron nails, but nails are nails -- you can use bronze nails, wooden nails, whatever. $\endgroup$ – AlexP Aug 4 at 19:28
  • $\begingroup$ @AlexP Doesn't wood have a warping issue and other problems too? I was under the impression that wood is a poor choice of material when you have arguably better options like iron/steel, bronze. Which is nails today are almost always metallic objects. $\endgroup$ – Theexurbmm10a Aug 4 at 20:01
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    $\begingroup$ Wood does have problems with warping etc. This matters when the object is intended for long term use, which ancient Greek and Roman artillery was not. On the other hand, wood is all around, easy to get, and easy to repair in the field. Siege engines were typically made on the spot, when needed; the Romans did not haul big machinery around on campaign -- they made them where they were needed. (This is the antiquity we are speaking of; overland means of transportation were simply not up to the task.) $\endgroup$ – AlexP Aug 4 at 20:26
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    $\begingroup$ @Matthew The myth busters catapult only fired about 120-150 feet whereas similarly sized medieval and ancient catapults could fire anywhere from 900-1500 feet. When you design a good catapult, things move much faster; so, the materials experience much more strain Roman era torsion catapults were especially powerful for their size and would have certainly shattered when fired if you only made them out of wood and duct tape. $\endgroup$ – Nosajimiki Aug 5 at 2:44
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    $\begingroup$ @AlexP That was true of Medieval catapults, but in the Roman Era, not so much. Roman torsion coil catapults were smaller and more powerful for their size, but they required materials and precision parts that are much harder to improvise including the Modiolus and Epizygis mechanism that made torsion coil catapults possible. Roman legions would typically travel with 9-10 heavy artillery pieces, and 40-60 smaller ones. $\endgroup$ – Nosajimiki Aug 5 at 3:01
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Yes, and they did

Not only is it possible, but many Roman catapults specifically were made with bronze and/or brass (not just iron). While bronze may be a bit softer than iron, the ancients were pretty good at work hardening it so that it could have a level of hardness similar to mild steel. Add to this the fact that it was much more resistant to corrosion, there were many cases where bronze may have been preferred for its ease of maintenance.

The unintended side-effect of removing iron

As your civilization develops, your people may also learn to work with nickel. On Earth, nickel is very hard to find in its pure form because it's almost always mixed in with larger amounts of iron, but when you remove iron from the equation, pure nickel will become about as readily available to your ancient civilization as copper. This will give them early access to copper-nickel alloys which will be both cheaper and stronger than bronze. Or, you could have them use bronze-nickel alloys which have very comparable properties to hardened steel.

Nickel has a slightly higher melting point but a lower forging point than iron, and a significantly higher melting & forging point than copper or tin; so, its use in the ancient world would likely follow along the same curve as iron. Bronze may be preffered at first due to the difficulty of melting Nickel, but once your civilization gets better at making high temperature forges, you will likely start to see its usage follow a similar path to the iron age.

Why you would not expect to find this world in our universe

In a world where bronze is readily available, copper and tin..etc are abundant while iron/steel aren't.

Just so you know, copper and tin are much more rare than iron because of how they are formed. Iron is the densest element that can be created from a net gain fusion reaction in stars; so, it is disproportionately common for its atomic mass because massive stars just stockpile the stuff up more than other elements. Furthermore, it is released mostly from exploding massive stars and white dwarfs which are much more common events than the dying low-mass stars and merging neutron star events responsible for the formation of Tin; so, the likelihood of a world forming with more copper and tin than iron is more or less impossible in our universe.

In Earth's history, the bronze age did not happen because iron ore was more rare, but rather that iron has a higher melting temperature which makes it harder to work with for more primitive societies. Most bronze age civilizations already knew about iron, but just lacked the ability to effectively work with it.

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  • $\begingroup$ Thank you ! So the idea isn't so far fetched after all, I will proceed with writing my story then. $\endgroup$ – Theexurbmm10a Aug 4 at 20:46
  • $\begingroup$ Ah yes I was somewhat aware of the impractically of such a thing occurring in the real world which is why I planned on setting it in a whole new different universe where things happen/work somewhat differently. $\endgroup$ – Theexurbmm10a Aug 5 at 8:51
  • $\begingroup$ But you could easily have a (regional) civilization that didn't have good iron ores. Consider how far the Phoenicians &c went for tin, or how most of the Americas didn't have useful tin deposits. $\endgroup$ – jamesqf Aug 5 at 18:37
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    $\begingroup$ @Theexurbmm10a -- You'll just have to come with a way to compensate for all that sciencey stuff. In one of my worlds, like yours, iron poor, I posited that the iron readily available near the surface was either eaten ages ago or mined and transported by Those Below down into more inaccessible depths of the planet. $\endgroup$ – elemtilas Aug 6 at 4:04
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    $\begingroup$ iirc the main reason iron took over from bronze was the cost became lower rather than material properties $\endgroup$ – jk. Aug 6 at 11:41
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In a word, Yes, they can be. It is not necessary however to use metals at all, just an advanced 'catapult'. Consider the trebuchet - only wood, rope, weight and gravity. Highly effective, very low overhead in materials, many could even be constucted on site during a seige. See diagram:

Simple Trebuchet

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    $\begingroup$ OK - but what if all we have is rope? What then? WHAT THEN?? $\endgroup$ – Willk Aug 4 at 19:25
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    $\begingroup$ @Willk You light it on fire and swing it around to toss it over the enemy encampent. Or you sneak into the enemy encampent and then tie them up and hang them with the rope. $\endgroup$ – DKNguyen Aug 4 at 19:47
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    $\begingroup$ This is actually a very nice homework project for high-schoolers. $\endgroup$ – Renan Aug 4 at 20:42
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    $\begingroup$ @Renan Yes and no, I got that assignment but my professor made the mistake of making throwing a tennis ball 25ft an "A" and every foot over that a bonus point. His only stipulations being it has to fit through the classroom door and it had to be a counterweight driven trebuchet.. I did not need to take my final exam to get an A+ as my final grade in that class. In other words, any teachers out there considering this assignment, remember to cap the score because a good design will be WAY better than the average. $\endgroup$ – Nosajimiki Aug 4 at 23:56
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    $\begingroup$ The trebuchet is very effective to launch nuclear shells. Read The High Crusade, by Poul Anderson. $\endgroup$ – NomadMaker Aug 5 at 0:44

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