Rogue said:
...really? Or is this an attempt at humor? If so, you must spare the dim-witted. If not, then please enlighten me with references.
Rogue
I think he's referring to Sean K Reynolds' comment that only things imbued with spells from the Enchantment school can be referred to as "enchanted." There's been a huge outcry on these board since he made the statement in a rant on his website (seankreynolds.com). Personally, the day I regard Sean's kind of drivel as "word from on high" is the day I let Forgotten Realms novels dictate what direction the campaign setting goes...

Regarding "enchanted" fortifications, there are lots of things you have to think about. There was a great article in Dragon Magazine many years back about some of the basics of fantasy-world castles. A lot of the article focused on the fact that you have people and things that can fly, and people and things that can teleport. Definitely two things you need to think about.
I allow structures in my campaigns to prevent Ethereal interlopers if they incorporate gorgons' blood in the mortar, or lead sheets surrounding the rooms someone wants protected. Lots of "contingency" spells can be put into place to prevent unwanted invaders. And it's not unreasonable to assume various magical defenses, from tower-mounted wands of Magic Missile to "kill zones" designed to maximize Cloudkill spell use.
A lot of castle defenses, including those incorporated during construction and those added afterward, depend on the availability of magic in your campaign. I have a serious problem imagining mass availability of spellcasters capable of casting 4th-level and higher spells. This doesn't mean they don't exist -- just that they don't exist in great numbers and aren't likely to hire themselves out as simple "castle guards." I can imagine an elite unit of 1st or 2nd level sorcerers for attack and defense, both in a siege-setting and a typical battlefield-setting. I can even swallow the idea of a small, elite special-forces skirmish team of five or six 4th-level sorcerers (or even 3rd level wizards).
However, your typical spellcaster is rarer than fighter-types, and therefore less likely to be available for large-scale combat, including castle siege. I would think that only spellcasters of higher levels who have a special interest in the capture or destruction of a castle would get involved in a siege.
Even in a typical D&D setting, magic isn't cheap, and constructing a magic castle is far more expensive than a regular one. And with the vast majority of invading troops being Warriors and Fighters instead of Sorcerers and Wizards, magic armaments aren't so necessary -- especially if you have to keep a paid spellcaster on staff just to recharge your items.
From the point of view of a commander attacking a physically-impossible castle design, or one that has been significantly augmented by magic (gravity-defying as above, or other such designs) I would look into the possibility of employing one or two high-level spellcasters. I wouldn't bring them to the battle. Instead, I'd hire them to make me a boatload of wands of Dispel Magic. I'd hire expendable 1st level wizards or sorcerers (after all, there are a lot more 1st level wizards than 10th level wizards!) to wield the wands, and I'd just start pointing them at everything I see. If I'm attacking a tower that's three-times taller than medieval-fantasy engineering can usually allow, I know that eventually at least one of those Dispel Magic wands is going to knock out something vitally important to the structure's integrity. I can lay normal siege, and simply wait till some or all of the wall (or even the whole tower) collapses. Given that lots of enemy troops might die, or my whole job might be completed from the action of one wand-bearer, it's better to go that route first.
So, ultimately, other than some mobile defenses, and a few more passive methods of protecting a castle, I tend to think that heavy magical augmentation of a castle design isn't in the best interests of the builders.
Anyone have other thoughts?