It also depends on what you're defending against, as normal traps are useless against Titans/FBs. I tend to go for lots of cage traps for ordinary pests (goblins and such) and menacing spike trap arrays, usually with green glass spikes, but when I opened up for HFS I added candy ones as well. Airlocking drawbridges to contain really tough opponents is also recommended (I've never encountered a Bronze Colossus, but I assume you'd need iron or better to hurt it, but I think a cage trap will do to capture it. I'd check the wiki on that, though). You can then eliminate them with a cave-in trap that you build while the opponent is contained.
My experience from the single time I've used regular weapon traps was that they'd jam after killing a few invaders, so I'd say a 50 strong goblin/undead invasion will probably make it though (provided they actually continue, rather than standing and looking at a dead leader).
Now, you probably have no elves or humans, at least, and goblins and undead are not that likely after all that time, but you could exit, make a copy of your save, start up and retire your fort, and then look at reembarking at the same place to see what neighbors you have. Then exit, throw the save away, and restore the copy to continue.