I just thought of something that everybody seems to be forgetting: numbers. Throughout history, attackers have generally needed a numerical advantage of 2:1 or 3:1 or so to make them the favored side in a battle. A mature dwarven fortress has upwards of
one hundred and fifty potential recruits that can be pump-trained, drafted, weapon-trained, equipped, and deployed. Sieges of even three or four hundred goblins could be horribly insufficient to overcome a sufficiently zerg-tastic defense.
I hope to god that the army arc includes the ability for civs to not only generate decent-sized armies, but to
keep doing so. Knocking out one enemy force, only to find that doing so has depopulated half the continent would be pretty underwhelming.
Why would it be impossible? Also, whats the point in having siege towers or battering rams if the siegers wont be able to reach the gates of your fortress at all? Even if you do not build any moats or traps, fortifications + ranged units are able to beat off all invaders easily. I do not build moats or traps for example, and I never loose a single dwarf in the sieges....
If Toady goes through the trouble of coding things such as sappers, battering rams, etc., do you really honestly think that he won't put in
something to nerf one of the most blatant uberdefenses? Just like moats, walls, and traps, there's lots of stuff he can do to reduce the effectiveness of the very same "unbreachable defense" that you mention:
*If he puts in siege towers, he would probably make them actually do what real-life siege towers did and
protect attacking troops.
*Battering rams with a roof on them.
*Siege engines to knock away fortifications so that attacking archers can return fire.
*The very same sappers that everybody keeps talking about to do Trolls' job and tear away fortifications so that, again, attacking archers can return fire.
*Shields that actually
work.
*Hell, maybe even the Roman
"tortoise" formation.
And that's all on top of the option of just plain nerfing ranged combat outright.