Catapults alone are good enough technology to prove why the wall is an idiotic idea. The wall is an effigy anyway for Trump, while he may actually believe that it's a good idea, that's not how it functions in reality. It's an anchor, a symbol, a thing to point to that combats illegal immigration and is a symbol of nationalism.

Now Trump might actually think it's a good idea - and I actually think he does - so that's absurd. But realistically it operates as a political beacon, and one that's quite effective.