Getting back to how strong Abe's drakon are (discussed here and here), I finally talked to a friend of mine today about that iron door. He's a structural engineer, so I knew he'd be a great one to ask about the relative strength of iron and steel (specifically for compressive loads).
It turns out that wrought iron is even stronger than steel (for compressive loads only; not for tensile loads). This means that not only were the drakon stronger than any weapons made back then, but they were stronger than any WWII-era weapons also (non-nuclear division, of course).
How much energy are we talking about? Well, firing a shell at maximum power, the Iowa-class Mark VII guns used 800MJ (in 660lbs of smokeless powder). That's about 222kWhr. Given that that's not enough to power a fair-sized house for a month, that might not seem like a lot, but consider where the energy for it is coming from. It's coming from the food they ate. How much food would you need to eat to strike one blow that strong? About 3.35M calories (technically, kcal, but food labels in the US are labeled calories). Given that most people eat about 2500cal/day, that's enough food to feed 1338 people for a day. How long is that going to take to eat?
Update: On the plus side, that would be one hell of a weight-loss program, as it would take 818lbs of fat to be burned off at once. And if you don't have that much fat on you (and they don't), it would take a bit more than twice that much muscle to be burned.
Suddenly, saying that you're going to eat a horse doesn't sound like a figure of speech at all, does it?
And remember, they might well be stronger than those guns, given that they're damaging a stronger armor.
Now how hard does it sound like it'd be to keep them bound?
And is there any way I can beat this further into the ground?