Well, then. Bad juju was apparently summoned to put me in my place. I hadn't spec'ed my military to deal with undead (7 dwarfs, only one hammer dwarf who wasn't fully trained yet), so naturally necromancers siege my fortress in the fourth year without there being a tower as one of my neighbors. 37 undead just ravaged my military and then my fort, as I forgot to link a lever a while back. gg no re
Well... zombies also get tripled physical stats. Most zombies lack armor (armor/equipment/held items all fall off a parson when they die), so its not too bad. However... tower zombies have triple physical stats, armor, and immunity to pain/organ failure. On top of that, they have necromancers behind them that will reanimate severed limbs (and fallen dorfs). You -really- shouldn't use edged weapons (or spears) against tower sieges. Axelords can do alright... if they don't get swarmed AND you separate the necromancers from the main force.
Also, hammers aren't that great against undead. They are like the bastard child between a spear and a mace in DF: they are blunt (breaks bones and more effective with weight... silver hammers> steel ones/platinum artifact hammer > fucking everything), but all of that weight is concentrated into a small surface area (tiny hammer head). Thus, hammers penetrate the crap out of armor and often lead to one-hit-kills on hte first round when they smash helmets through people's skulls. They rely far more on the organ damage than pulping to incapacitate foes. This is why you use maces against reanimation. The mace keeps the zombie intact, but also breaks all their bones and pulps all their muscles. The zombie is rendered unable to move/finally dies. Think of smashing them into (rotten) jam.
Also, a squad of macemen alone is the worst weapon to field a full squad of. They are underpowered in that mace hits should liquify internal organs and shatter bones, quickly killing someone. However, they usually just bruise up skin/organs/muscles. After the target passes out from pain, the maceman then spends far too long pulvering the victim before they finally die. During this time... he isn't attacking anyone else. Swords, spears, axes, hammers all kill quicker and are thus preferred (for living targets). A special note on spears- very large enemies (megabeasts, titans, colossi, FBs) have skin/fat/muscles too thick for other weapons to pierce and reach the organs. Spears, on the other hand, are long enough to pierce through all of a hydra's flesh and reach its heart. Otherwise, your swords/axemen will be decimated trying to lop off all of its 12 heads+arms/legs while your mace/hammerdorfs waste time bruising so much superficial tissue. In general, the weapons all have their different places in your arsenal. Axes are the best at dismememberment, hammers work best against armored opponents, spears kill large beasts the best and are great for organ damage in general, maces are great to incapacitate for other soldiers/best for undead, and swords are a great all around weapon (personally I never use them though. Axes are more dorfy and dismember better, and hammers are better against sieges/equipped enemies).
Although... traps are probably your best defense. Not simply cage traps, but hte ones you have to engineer yourself. Drowning chambers are excellent mass-slaughter devices. Also, if you are dealing with amphibious/aquatic/undead invaders you can try to engineer a freezing chamber. I'm not sure if anything other than demons can survive being frozen. An obsidian-chamber is always available as well, but will destroy all the non iron/steel equipment and clothing (which could be a blessing, as it also destroys the bodies). You can fling/drop socks on invaders, drop them 20+ z-levels, create a ballista corridor ~150-200 tiles long that shreds attackers. You can set up a looping track of lead-filled minecarts... or you can just create a series of airlocks to break up enemy forces to ensure your militia is never out-numbered (I did this to fight the circus)