Can sieges withstand magical assault?

[Epametheus]

I'm looking at the SRD, for types of walls. I guess castle walls would be superier masonry or reinforced masonry.

A 1 ft thick, 10x10 section of superior masonry has hardness 8 and 90 HP.

BUt this is a castle. The wall are going to be a LOT thicker than 1 ft. So how about 10 ft?

Now we're looking at a 10x10x10 section of wall having hardness 8 and 900 HP. Assuming an average damage of 35 points from 10d6 acidballs, it'll still take 25 acidballs to breach that section wall (if it fails every single saving throw).

How much of an issue that depends on the resources of the attackers and the competance of the defenders. Do the attackers have 5 L10 sorcerers who all have Energy Substitution: Acid? Do the defenders have anything that could protect that section of wall (Like throwing a wall of force over it)?

Disintegrate can rip walls right open, but it looks like objects get a saving throw now. Layered walls would definately be the trick for dealing with it -- two 3ft thicks and one 4ft thick section, for 2 270 HP sections and one 360HP section. Still takes just as much firepower to get through.

Even once a breach is made, the battle isn't over -- the attackers still have to defeat the evenly-matched defenders, after expending all of the firepower necesarry to punch through the wall. Depending on the tactics of the defenders, trying to pour through a breach may end in disaster for the attackers (readied action: blade barrier against the charge, for example).

It's much better for an elite squad to inflitrate the castle, slay key people, and open it up from the inside, than to try to defeat it in head-on combat.

 

[kigmatzomat]

A 1 ft thick, 10x10 section of superior masonry has hardness 8 and 90 HP.
BUt this is a castle. The wall are going to be a LOT thicker than 1 ft. So how about 10 ft?
Now we're looking at a 10x10x10 section of wall having hardness 8 and 900 HP. Assuming an average damage of 35 points from 10d6 acidballs, it'll still take 25 acidballs to breach that section wall (if it fails every single saving throw).

A quick googling results in several fortresses with walls 20' thick and a vietnamese fortress had walls 37 feet thick. Imagine punching through 3,300HP. What is that, 95 acid balls or 4 disintigrates where all saves were failed? (20 disintigrates if you wanted comparable breeches) At the point of throwing 20-100 spells to create a single breach you've just tossed yourself into the "mystical high artillery" situation where you have mages throwing spells for several minutes straight. Admittedly, that was the imperial fortress but a series of 3-5' thick walls with 10' gaps between them, some filled with sand or earth, would ablate a *lot* of magic and be completely mundane.

Even once a breach is made, the battle isn't over -- the attackers still have to defeat the evenly-matched defenders, after expending all of the firepower necesarry to punch through the wall. Depending on the tactics of the defenders, trying to pour through a breach may end in disaster for the attackers (readied action: blade barrier against the charge, for example).

It's much better for an elite squad to inflitrate the castle, slay key people, and open it up from the inside, than to try to defeat it in head-on combat.

People forget that if a mage makes a breech the ground pounders still have to get inside. Neither mages nor aircraft hold ground; it takes infantry.

In other words, even if Saurumon blows open the doors, the orcs will be hit by arrows & siege weaponry before getting inside and once inside they will be fighting against foes who know the territory and likely have reinforced or barricaded the interior regions to make going slow and painful. The defenders' reinforcements won't be suffering the way the attackers' will be so it will require far more men.

Stealth and assasinations are the way to to go but that's why virtually every head of state has official imposters to take that first bullet or three. It's not that they're magically disguised or even wearing facepaint, they really look like the king. Heck, the only decent part of Episode I was Amadala having a bodyguard play queen while in enemy territory.

 

[Whizbang Dustyboots]

Designing a castle smarter -- like the New World example given above -- coupled with treating selected areas like magic items (not the whole castle, perhaps, but it would be worth spending more on the keep, for instance) could certainly make the castle a viable fortress.

 

[Saeviomagy]

Just a point on the high level magic.

Most of the effect of high level spells will be: Stuff the armies already have in place.

Wall of iron
Simulacrum (remember those beholders? Meet D&D heavy artillery, on both sides)
Clerics make the 'cause disease' and 'starve em out' parts of a siege irrelevant
Permanency: A permanent solid fog around your castle makes conventional siege engines worthless, and prevents the targeting of spells from range, forcing your enemy to close with you to attack. A gust of wind gives them 10 minutes to make their attack unless you fill the gap again. Symbols of persuasion are particularly nasty defenses - suddenly half your army decides they quite like the renegade... Naturally dispels fix permanency, but then that's taking away from the attackers resources quite heavily.
Nightmares being tossed back and forth between the attacking and defending mages will be common, denying both sides restful sleep.

And finally, when you do get in, you've got guards and wards to contend with.

All in all, I think the advantage goes to the defenders - primarily because they have the benefits of preparation, and one of the biggest effects of a siege has been totally nullified.

 

[Elder-Basilisk]

A lot of people here are long on theory and short on actual examples. I had the interesting experience of playing out the final assault on a fortified city using only slightly modified D&D rules. Here are some things I noticed:

1. Disintegrate is overrated by far. The walls of a heavy fortification will be very thick. So, it will take multiple disintegrates to get through. Furthermore, when you do get through, you have... a ten foot wide tunnel. That's not enough to bring an army through. In large scale battles, a hole in the wall that two soldiers can walk through at a time is not a really big deal. Try to use it and you'll end up with hundreds of soldiers standing outside the wall, waiting for the front line to clear room for them.

2. The importance of spell range is dramatically underestimated and the significance of small area effect spells is dramatically overestimated. A composite longbow has a range increment of 110 feet. Heavy crossbows aren't much worse. That means, that, in order to cast any spell with a range other than long, you need to spend several rounds moving through the field of fire to get in range. Even hitting only on 20s, 200 archers will deal a lot of damage.

Similarly, in a best case scenario, a fireball will take out around 40 soldiers. (In a realistic scenario, it's a lot less since they won't be so tightly packed if they can help it). If the combat measures thousands on a side, that's not going to change the course of the battle. Even if it's only hundreds per side, it's not an "I win" card. A unit of 100 archers will generally take out a similar number of enemies (especially if buffed with high level bardsong, or Flame Arrow). And they've got more staying power and are cheaper than the wizard.

It's only the really high level magic--Cloudkill, Sunburst, Holy Word, Firestorm, etc that changes the course of a large scale battle.

3. The effect of mobility spells is also overestimated. They can play a large role in small engagements and special operations, but you're not going to dimension door enough troops onto the walls of a fortified city to do anything other than maybe hold out against the hundreds of defenders--especially if some of those defenders are also high level characters.

4. The synergy between high level characters and low level troops is often overlooked. Flying, invisible wizards with wands of fireball sound good.... until you consider that one mid level wizard with see invisibility, glitterdust and a squad of fifty archers makes that a recipe for a flying, invisible, and dead wizard.

5. The influence of clerical healing magic, etc. is over-estimated. Sure, mid-level clerics can create food and water. But they can't create enough for hundreds of people. They're limited to dozens. Create water and purify food and drink are less limited since it's zero level and the ratio of 1st level clerics and/or adepts to population/army is a lot higher than the ratio of level 5 clerics to population/army. Remove Disease suffers from the same limitation. (Especially since a lot of diseases can spread before people show symptoms that would enable clerics to cure the initial victims of the disease). They will all have an effect, but it only makes starving a population out harder--not impossible.

6. Nobody's mentioned the effect of DR here either. Units, individuals, or summoned creatures with DR are at a huge advantage on the large scale battle because they are less vulnerable to cheap and effective mass ranged attacks. A fighter with great cleave and armor of invulnerability will cut a much longer swath through his foes than a fighter with only great cleave. (In fact, really high level warrior types will mow through ordinary soldiers like Achilles in the Illiad and can generally only be stopped by heroes of similar stature... or a thousand guys with bows (50 hits including 2.5 crits, even if they need a 20 to hit=52.5d8+ 52/5x bardsong bonus, etc). High level summoned elementals are also a very significant factor on the battlefield (though they can be neutralized with magic circles).

7. One thing that nobody has yet mentioned is the effect of magic that makes fortifications easier and quicker to build. A high level character with wall of stone can erect a small fortress overnight. Move Earth enables a character to construct massive earthworks very quickly. I didn't see very heavy use

After that experience, my thought is that D&D magic has the greatest effect on small to mid-scale engagements. The border fort and the small castle fare far worse than Ninevah, Troy, or Krak des chevalliers. Thus, while I would expect some of the effects of the age of canon to recur in a D&D world, I think that small scale engagements would see more changes than large scale ones.

 

[kigmatzomat]

After that experience, my thought is that D&D magic has the greatest effect on small to mid-scale engagements. The border fort and the small castle fare far worse than Ninevah, Troy, or Krak des chevalliers. Thus, while I would expect some of the effects of the age of canon to recur in a D&D world, I think that small scale engagements would see more changes than large scale ones.

I agree. The major fortresses are going to be just as hard a nut to crack. But the "keep on the border" is going to be like the Bradly IFV: tough enough looking to draw fire it can't survive. Anything that can't afford layered walls will be easily breeched by a magic- or monster-equipped foe.

IMC I've phased out the single-tower castle with the standard 3-5' thick wall. Too much expense for too little protection. These days the wall is usually backed with earth to make it much harder to breech. The tower has been reduced to a stone ground floor with a wooden tower faced with leather or thin copper plates to make it resistent to fire arrows. Now the towers are to provide supplies for the roving troops and act as a signal system rather than any kind of hardened base of operations. It'll hold up to most of the roaming orc and goblin hordes but will fall only slightly faster to a caster than its significantly more expensive brethren.

 

[Ace]

If it takes 95 Acid Balls to destroy a castle wall -- thats what 2 wands ? Not that much magic for alarge army -- Just get 10 or 20 wands and punch holes through the wall or use disintegrate to tunnel under the castle

Or if the enemy is holed up in the castle teleport your elites into the countryside and trash the crops -- The Chauche (sp?) is likely to be very effective -- No you can't get the king and his knights but a fewof you teleport squads can destroy every forest and crop in the kingdom

Another nasty option is to go EPIC -- a rain of colourless fire or meta acid or whatever would do 1pt per round -- 1200 points of damage in 2 hours to everything within a 2 mile radius

 

[MoogleEmpMog]

One, as others have pointed out, strong defenses against magic covering an entire fortress are prohibitively expensive. As the French learned with the Maginot Line, that money would probably be better spent on some strong, mobile, offensive forces instead.

Actually, the Germans just end-arounded the Maginot Line because the French "learned" that their money would be better spent on non-military expenditures before the line was completed.

By the end of WW2 the Line was essentially useless because its guns were too small to be effective against tanks at long range. But one could make a strong case that a completed Maginot Line in accordance with the original specifications would have effectively stopped any land war prior to 1942. With comparatively inexpensive upgrades, it would have remained serviceable into the '60s at least, barring nukes.

-end tangent-

Overall, I agree with Elder Basilisk. Mundane defenses, designed with a reasonable consideration toward magic, can stop most spellcasters dead in their tracks. With defensive spellcasters along for the ride, it's simply no contest.

 

[rounser]

If it takes 95 Acid Balls to destroy a castle wall -- thats what 2 wands ?

And while the besieging wizards are concentrating on destroying the walls with their wands, 95 acid balls from the defending mages and their wands takes out how much of the besieging army?

 

[Romnipotent]

Magical seiges can withstand it. The whole idea with seige assault is to distract them while you dig in, fly in, or otherwise sneak