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What would be the best wall profile and size for a prepared anti-zombie fortification? I am trying to protect against fast zombies like the ones in the movie adaptation of World War Z, who can climb over each other, so take that into account.

Here are some profiles I've considered.

wallprofiles wallprofiles2

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    $\begingroup$ Can't prevent. At best you can maximize the number of Z it takes to overcome the wall, for a given amount of material. So you probably want an inverted L. The horizontal should be enough that the zombie pile can't use the wall itself for stability, meaning they need a full pyramid rather than half of one. Aside from that, you really just want more height. The higher you go, the more of them it will take. You still need a way to clear them away as they accumulate. $\endgroup$ – Bryon Mar 24 '15 at 14:49
  • $\begingroup$ @BryonDowd crushing the zombies with the rocking wall will certainly work. ;) $\endgroup$ – Isaac Kotlicky Mar 24 '15 at 14:56
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    $\begingroup$ WWZ zombies were slow and dumb. There was a movie by the same name that had 'fast' zombies. $\endgroup$ – GrandmasterB Mar 24 '15 at 16:49
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    $\begingroup$ Some of these wall shapes are highly improbable -- hard to build and not very useful, so why would you? Can you either narrow this down or explain why you think all of those are reasonable options? I also think this is too broad because of all the different types of zombies you want to cover. Please edit to address these issues. Thanks. $\endgroup$ – Monica Cellio Mar 24 '15 at 19:43
  • $\begingroup$ I made an edit to try to make this question more clear, with all the required info up front. I added size as a consideration, as mere shape doesn't help until you address height (especially since you brought up climbing). I personally don't think the picture adds anything (it seems pretty random to me), but that's your call. I'll reopen. $\endgroup$ – Monica Cellio Mar 25 '15 at 20:50

12 Answers 12

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Wall features

When selecting a wall you need to consider:

Structural strength

You need a solid, wide base that will hold against pressure of thousands of bodies. You need strongpoints to make it rigid and stable. You need the thing to be literally immovable. So, diamond, inverted triangle, vee, bowl, ellipse are all ruled out.

Space for battlements and other structures

In short, you need to be able to stand atop comfortably and without being a target. So, the best way is it have at least some flat top. I assume you would place some crenellation to secure combatants.

Shape of the wall that faces the enemy

Well, you would have three options. Triangular is the easiest to build and has the most strength, but since you wouldn't face artillery it is not a problem. Straight wall is OK if you don't face an enemy with scaling ability. Inverted slope is great for combating ladders and such, but does not give you a great fighting opportunity. What you need is a straight wall with overhang - machicolation. That would give you defense against climbers AND reduce your blind spot. That would make your exterior look like inverted L with very short horizontal platform bit.

Shape of the wall that faces you

Ideally, you want easy access. A slope is perfect, and it adds to your structural strength. It's easy to make stairs or platforms and you can build on top.

Final shape

Wall drawing

Any type of zombies would have a hard time breaching it. Your greatest problem are the flesh towers of World War Z, but such a design would take care of it by dropping anti-infantry explosives right near the wall using machicolations (dashed line), and wall's wide base would be able to withstand that quite well, as long as you stick to regular anti-personnel grenades.

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  • $\begingroup$ Your answer does a better job at explaining it, but why not just mine the land around your walls? It wouldn't kill the Romero/Brooks zombies but it would effectively render them a nonthreat. $\endgroup$ – the_OTHER_DJMethaneMan Mar 24 '15 at 15:47
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    $\begingroup$ Sure, that's an expansion of the idea. I tried to stick to the "best wall" question and describe a wall, and specifically from cross-sectional point of view. If we're talking about fortification principles in general we need to consider such things as wire obstacles, moats, ditches and counterscarps, just to cover the basics. Then we have to discuss towers, strongpoints and keeps, layout and shape of a fortress and the principle of defence in depth. That would be far out of scope of the question. $\endgroup$ – eimyr Mar 24 '15 at 15:58
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    $\begingroup$ Mines are kind of a use once defense. They'd all get tripped in the first wave, kill a few, make a bunch of crawlers, and then no more mines. A crawler is worse than a walker. A crawler would be hidden by tall grass, and in a throng of walkers would be biting at your ankle where you wouldn't be expecting an attack. $\endgroup$ – AndyD273 Mar 24 '15 at 16:03
  • $\begingroup$ @AndyD273 You could always plant more mines after a massive horde attack or build pit traps that build a moat of the undead---that last idea would protect you from raiders for a while. $\endgroup$ – the_OTHER_DJMethaneMan Mar 24 '15 at 16:15
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    $\begingroup$ @DustinJackson I wouldn't want to run out and plant more mines. Something you can throw would be better, like a grenade, maybe with a proximity trigger. Pits would work until they filled. I'm mostly just picturing the Z ramping up the 200 ft tall walls of Jerusalem in the WWZ movie. In the WWZ book (which is better if you haven't read it) there is a guy that explains the math of killing Z. An explosion has little effect because Z are not effected by over pressure. One bomb might kill 50 Z. A sharpshooter with a box of bullets could kill 1000 for hundredth of the cost/materials. $\endgroup$ – AndyD273 Mar 24 '15 at 16:26
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eimyr has by far the most practical wall design. My only problem with it is that it requires the use of consumables like grenades and bullets.

Depending on how prepared the defenders are and how much they know about the enemy they'll be facing they'd want to design the shape of their perimeter as well.

Mainly they'd want some kind of resilient system that can dispose of arbritrarily large numbers of zombies without clogging or leaving a mound that can be climbed.

Hence you might want to funnel them towards a point in your defences with a transparent barrier behind which is a delicious looking human. In front of the barrier you have a large pit or trapdoor that drops into a rock macerator salvaged from a quarry.

enter image description here

This would allow you to keep the population of zombies outside your walls low without always needing to expend bullets or grenades.

Zombies drop into the almost unclogable rock macerator and are crushed into pulp. No fuss.

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    $\begingroup$ this is ... gross :P $\endgroup$ – Jorge Aldo Mar 24 '15 at 17:29
  • $\begingroup$ Given the zombies'speciality of human wave (pun intended) attacks, you would need to make sure you have damn good sewers to clean the zombies remains... otherwise, at some time they could as well just walk on the resulting pulp. youtube.com/watch?v=RicaXxiU1WM $\endgroup$ – SJuan76 Mar 24 '15 at 17:33
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    $\begingroup$ The power used to run the macerator is a consumable as well. And would likely be in shorter supply than ammunition or explosive would be. $\endgroup$ – Shane Mar 24 '15 at 19:52
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    $\begingroup$ @Shane Not necessarily. $\endgroup$ – KSmarts Mar 24 '15 at 20:50
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    $\begingroup$ @Shane good point but I believe if you were choosing a site for your zombie-proof compound and had time to prepare you'd pick somewhere with a reliable source of power like a fast running river.(which also might help to defend part of the perimeter.) Then you'd only need consumables for backup generators. $\endgroup$ – Murphy Mar 25 '15 at 10:30
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Similar to Murphy's idea, the best shape of wall is a purely vertical one. Only, instead of being made out of stone, you'd make it out of shredders.

You could orient it either as seen below, so that the zombies will be converted into red paste upon scaling over the sides, or with the grindy bits pointing out, so that they get converted into red paste as they push up against it.

enter image description here

This model of grinder even has a drainage spout, so you could capture the zombie paste, which I imagine probably makes good fertilizer. Or failing that, the ultimate in biological warfare stocks. Why only funnel some zombies into a slaughter funnel, when you can make your whole wall a zombie grinder? And it's a modular wall design, which is all the rage these days. Plus, eco-friendly, because you can... erm... "recycle" the zombies paste into either fertilizer or bioweapons.

Also, importantly, this kind of device is surprisingly common (even been to a farm - combines, threshers, etc.) and would be both easy to salvage and of otherwise limited utility in a zombie-pocalypse. You wouldn't find much in the way of farming or mining activity beyond the safety of a city's walls, and the various urban uses for large grinders and crushers (like crushing cars and compacting garbage, or even mowing lawns) would probably have almost no demand, so it seems to me like it would be fairly economical to turn this otherwise useless machinery into a practically impenetrable zombie defense. It certainly seems to me like it would be at least as easy to rig up a wall of grinders and shredders as it would be to construct a whole solid wall, which would require enormous amounts of stone or cement (etc.) to construct.

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  • $\begingroup$ Not sure about the fertilizer. Don't want to infect your food supply, depending on whether that is a means of transmission. And remember the mass of your slurry coming out is the same mass of the horde that went in, so you've got to transport it somewhere out of the way quickly, since your grinder will either jam or spit material out the way it came in if the drain gets clogged, eventually leading to safe passage over it. My guess is you would need to wash the sludge out to sea, probably using a river or some-such. $\endgroup$ – Bryon Mar 24 '15 at 19:20
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    $\begingroup$ @BryonDowd I feel safe in saying that if you have to worry about grinding up enough zombies that the zombie slurry is jamming your grinders, you have bigger problems, like that the zombies are reproducing like Tribbles. You'd have sharpened your blades down to nothing before zombie slurry accumulates in sufficient quantities to be an issue. Plus, there's that old adage "the world needs ditch-diggers too" ... no reason to think it wouldn't apply in zombie-pocalypse times. The zombie slurry pile is getting high... send Jimmy out to expand the zombie slurry ditch again. $\endgroup$ – HopelessN00b Mar 24 '15 at 19:33
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    $\begingroup$ You could mount these on the front of remotely controlled vehicles which patrol the perimeter, deployed when zombies are threatening to create a pile to overcome the wall. Also, fit the outlet with a snowblower to fling the waste as far away as possible and possibly knock away the approaching zombies. $\endgroup$ – Turophile Mar 26 '15 at 12:23
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This is yet another fun idea ruined by engineering and economics.

Engineering

Different shapes sound fun, but keep in mind that any variation away from simple has a cost. It's either going to cost you height or structural strength, and both of those are incredibly important. There's a reason human walls are, traditionally, giant rectangles - it's because giant rectangles work.

Economics

On top of any engineering concerns, consider that you generally have limited materials to work with. Using extra materials for a different shape is going to cost you height or area (you can enclose a larger area with simple walls). Also consider that bracing the wall from behind has diminishing returns - you're not getting as much out of that material as the original wall strength, especially if smart zombies decide to pull instead of pushing.

Layered Simple

Even if you do have tons of extra material, it might be better to consider alternative approaches. Why not have two simple walls, with a gap in between? There's a limit to the height you can get with one wall, depending on the material, but you can build multiples easily enough.

I suspect that having multiple basic walls is going to win over any single complicated wall, if they're approximately the same cost and effort. This helps negate the piled zombies because they have to do it twice, and gives you a fallback position. If there are times the zombies aren't attacking, you can use that to re-take the outer wall and clear any piles away.

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  • $\begingroup$ Historically the walls of forts weren't rectangles, they were wider at the base. $\endgroup$ – Jack Aidley Mar 21 '17 at 11:46
  • $\begingroup$ I think multiple walls is definitely the right idea. The taller you make a wall, the thicker you have to make it. Meanwhile it becomes harder and harder to add additional material to the top. Once you hit a certain height, a sheer surface just becomes impossible. $\endgroup$ – Fhnuzoag Mar 21 '17 at 13:51
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Most answers are concentrating on scalability and weapon placement. Weapon placement is very important, and I'm a personal fan of the auger-shredder, but the question is about walls and survivability.

The greatest danger is from the WWZ zombies, all others are of the same sort, but less danger, so I'll concentrate there.

In the movie, Jerusalem was doing remarkably well with just tall and straight walls. God knows where they resupplied ammo and fuel, but the walls were suitable until

people inside started chanting and drew all the Zs to one place where, as has been said, any shape wall would have eventually failed. Shooting 90 zombies in the head turns them into stairs. (Sorry for the convenience.) !

The problem being ignored here is the interior shape of the wall, and specifically

its acoustical value. If the Zs outside never heard the chanting, the city could have lasted for years. Ideally, you would have a concave surface so that sound waves produced inside the city are directed upward, however, of the choices listed above, the V-shaped is the best mix of non-scalability and sound proofing. The bowl shape would be perfect if the city were inside the bowl. Of course, I'd want it tall and wide.

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  • $\begingroup$ +1 for "Sorry for the convenience." We apologize for the fact that you can still get up there. $\endgroup$ – KSmarts Mar 24 '15 at 17:34
  • $\begingroup$ Sorry to say it is stolen: quotationspage.com/quote/39411.html $\endgroup$ – IchabodE Mar 24 '15 at 17:36
  • $\begingroup$ Yeah, I know that. $\endgroup$ – KSmarts Mar 24 '15 at 17:37
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Give the wall a steep incline and grease up the surface facing the zombies. This is way easier to describe with examples (and please excuse the crappy photo---I am using a crappy photo editor). I am also well aware that this isn't the best answer because I am pressed for time. enter image description here

The steep side is the side the zombies will face. You will need a pretty tall---i'de say fifty to a couple hundred feet---to stop a large group of undead. Grease the side facing the zombies with oil of some kind and they can't get up. As they go Max Brooks on the wall and begin to stack up they will hit the ramp. This will give them another obstacle and the horde will have to become big enough to expand out wards. Most would fall and the few who mad it would be easy targets for any guys you have up there to pick them off. See below.

enter image description here

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For most Z types, the triangular inverted or L inverted seems like they would be the best. No hand holds, climbing an overhang is tricky, and ramping up would be made more difficult by it as well, as towers of Z would tend to tip. Inverted L would also allow you to have Murder Holes. I'd also like to propose a new shape, the \ (backslash). Basically the V without the inner wall. Same overhang as the inverted triangle, but would allow you to put arrow slits in... if you add a bit of an overhang like the inverted L with murder holes it could be interesting.

The tricky ones are the WWZ movie type, as you've said. The inverted triangle would still slow them down a bit, but once the concave area is filled it wouldn't be much different than a normal straight up and down wall. So for that type you almost have to have active defenses and not just passive walls. Something to remove the base. I think it could be as easy as putting flame thrower nozzles every 10 feet along the base, and when you start to see a bunch begin to ramp up you just turn them on along that section, burn the base away and the tower topples, plus since they are so congregated you'd remove larger numbers, thinning the ranks. Also have a bunch of phosphorus grenades along the perimeter. That stuff burns underwater.

I always wonder why fire isn't utilized more in the movies. Maybe Z don't burn very well? Destroying the brain is the only way to kill them, but burning the muscle would stop them moving, and fire would cook the brain...

A giant auger would work well, chopping any Z that gets close to pieces and pulling the pieces along the wall to disposal areas. Could get clogged though.

Another active defense would be something like a giant captive bolt gun.
Something that shoots out and smashes zombies, but doesn't take ammo, and can be powered by compressed air. fairly short range, but they are coming to you... Could be combined with murder holes/arrow slits.

I actually just started the walking dead last night, and they almost seem smart. I saw tool using and basic reasoning, at least in the first 3 episodes.

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  • $\begingroup$ Further along (4th season) you'll get to your answer regarding walkers and fire. $\endgroup$ – IchabodE Mar 24 '15 at 16:35
  • $\begingroup$ @MBurke Gotcha. Probably responding to the same criticism, and "We wanted the show to last longer than 1 season" wasn't a good enough reason... Bodies can burn, that's why pyres are a thing. $\endgroup$ – AndyD273 Mar 24 '15 at 16:41
  • $\begingroup$ Bodies burn, but not easily. Takes a lot of fuel to burn a body, so probably not efficient. $\endgroup$ – Bryon Mar 24 '15 at 18:59
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Interesting... This can operate via a process of elimination... Upright triangle is right out - it's the easiest to climb.

Assuming climbing fast zombies, upright L offers zero advantages over a simple wall.

The inverted L and T walls are identical - no real advantage to have an overhang on the defending side like that. Both of those would do a good job preventing climbing (until a large enough group formed a pyramid) but you can't attack zombies at the base of the wall effectively. If enough get into that dead zone, tunneling under would be trivial. So they're out.

C shaped would mitigate the threat of tunneling, I suppose. This might be a good option.

I fail to see the point of the cavity for V and bowl shaped walls, other than forcing them to climb a little bit more and being more complex to build and maintain, as well as structurally more frail. They are otherwise identical to the inverted triangle. So they're out.

Diamond shapes provide a good visual angle to attach most of the approaching horde, but would be easy to climb if enough got into the blind spot.

The ellipse has a minimal blind spot, wide viewing angle, and is hard to climb. So funny enough, I'm going with the ellipse with the following caveat: That the wall be built in sections that can "rock" back and forth. Basically you can use this to "shake" climbing zombies off and crush the ones at the base into paste.

You would think that a bowl would work for that, but when you tilt the bowl, you actually make it EASIER for the zombies to climb up the rim into the inner hollow.

The ellipse would work way better and people on the top would still be able to defend when it rocks - just provide firing stations with seatbelts to keep them in place!

Additional caveat/update:

To clarify, there would be a backstop on the defender's side of the wall to prevent it from rocking backwards or being pushed over. A hydraulic system would push/rock the wall slightly outward from the top, crushing any buildup at the base and shaking off any zombies attempting to climb. Since we only need to rock, say, ten degrees for each section, no gaps in the perimeter will open up. you might even be able to use the zombie slurry as a bio-fuel starter to power generators for the defenders.

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  • $\begingroup$ Amusing, but how do you rock a wall without opening some point on the perimeter? $\endgroup$ – Bryon Mar 24 '15 at 14:52
  • $\begingroup$ @BryonDowd If it's tall enough and the rocking is only a couple degrees, there would be significant overlap between the sections. Not a problem. $\endgroup$ – Isaac Kotlicky Mar 24 '15 at 14:55
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As Loren said, wall design is only a part of the solution. Any tall wall, with a smooth surface will be the defining obstruction of a 'wall'. To create a more robust design to repel ZOMBIES, additions need to be made.

Starting with the wall from world war z; the problem lies in the mass of zombies being triggered by the loud noises, and building their own 'wall' to compensate the walls in place.Adding on to the assumed 'best' wall design; having large, extensible plates that can be automatically/ manually pushed outwards, to disrupt the horde tower being built will protect from this problem.

Another design would be to create triangular parts of the wall; this will not allow the zombies to focus on a single area. And by adding additional plates will allow the multiple towers of zombie hordes to be continually disrupted.

Almost like this.

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  • $\begingroup$ Welcome to worldbuilding! As this is only an addition to the best wall design (although it is a good idea), it doesn't (yet) answer the question. As such, would you be able to extend this into an answer that explains what the overall design would be, including your extensible plates as part of the design? Thanks $\endgroup$ – Mithrandir24601 Feb 26 '17 at 23:28
  • $\begingroup$ I hope this 'answers' the question. :) $\endgroup$ – Mattcul Feb 26 '17 at 23:39
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The shape of the wall will be mostly irrelevant. You want it to be strong and high, but most of all you need a way to counter any piling up of ramps, be they made of any material or of heaps of zombies.
Automated flamethrowers should help you there.
Other than that, make your walls hard to reach: Crocodiles in a surrounding moat might be a direction you could think.
In general, several lines of defence should help you, but at least one of them needs to have active components. Otherwise sheer masses will scale any wall.

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  • $\begingroup$ Z don't breath, so moat would be less useful, and they'd overwhelm and eat the crocs. I think some kind of auger would work better. Any Z that gets close to the wall gets pulled in and chopped to bits. I agree on the flame throwers, even if they aren't automatic. I always wonder why fire isn't used more against Z. Probably would end the movie to quickly... $\endgroup$ – AndyD273 Mar 24 '15 at 16:00
  • $\begingroup$ @AndyD273 Good point about the breathing and the crocs. A strong acid in the moat, then, maybe? Liquid Zeds don't pile so well? $\endgroup$ – Burki Mar 24 '15 at 16:06
  • $\begingroup$ Acid would work well, especially if you have a way to filter and freshen it. I don't know how many bodies you can dissolve in a standard drum before the acid gets to diluted. Also, I don't know how fast that stuff dissolves flesh. It could be that they'd be able to pile faster than the bottom ones melted. Doing more research might be tricky. $\endgroup$ – AndyD273 Mar 24 '15 at 16:12
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    $\begingroup$ @AndyD273 What? are you afraid to google methods to melt bodies? Don't want that in the browser history, eh? $\endgroup$ – Isaac Kotlicky Mar 24 '15 at 18:28
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    $\begingroup$ @IsaacKotlicky Yeah you know, you start out by searching for body disposal methods, and then one of your neighbors goes missing, and the police start asking questions and it's like, "Hey, I know I complained about the parties and noise a lot, but I didn't hate them. I was just doing research for a story." But they are never found, and even though there is no evidence, people always have that question in the back of their mind... "What kind of research?" $\endgroup$ – AndyD273 Mar 24 '15 at 19:14
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I don't think most of these shapes create any advantage. Some are clearly inferior---anything sloped provides some support for a pyramid that a straight or inverted wall does not provide.

As others have said, World War Z movie zombies (not the book zombies!) are the greatest threat, anything that can stop them can stop anything else.

Jerusalem almost got it right--simple, tall walls. Their mistake was not making it tall enough to defeat a pyramid attack. I disagree about defenses--the wall should mostly be a passive defense. If you're using weapons you can run out.

Another 15' on the Jerusalem wall would have stopped anything short of a huge mass of dead bodies that the zombies simply climbed.

I would also be looking at trapped breeches. For example, let them into a cage--when the cage gets heavy it's anchors let go, it falls down on a huge mass of spikes--when it falls the breech is sealed. It falls to a point that's underwater and accessible to ocean wildlife--let them come in and eat the zombies. When it's been cleaned up enough it's counterweight lifts it back into position. (The spikes are only underwater so even if the zombies offer enough resistance that they don't go all the way through and stop it's fully dropping it's still in a position for them to get eaten.

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  • $\begingroup$ Their main mistake is not the height, it is the lack of bastions or other ways of killing zombies without using loud helicopters. $\endgroup$ – eimyr Mar 24 '15 at 17:49
  • $\begingroup$ @eimyr If you're relying on weapons you'll run out of ammo. $\endgroup$ – Loren Pechtel Mar 24 '15 at 17:50
  • $\begingroup$ @LorenPechtel there are a limited number of zombies. Mass tower attacks are unlikely to occur often. A couple napalm bombs or similar are very cheap to stockpile and would have rendered this mode of attack impossible. $\endgroup$ – NPSF3000 Mar 26 '15 at 10:13
  • $\begingroup$ @NPSF3000 The problem is when you kill zombies you attract more zombies in the process. $\endgroup$ – Loren Pechtel Mar 27 '15 at 1:40
  • $\begingroup$ @LorenPechtel good! Then use this to attract and kill 'em. After all you will be wanting to leave your fortification at some point and the fewer zombies around the better. $\endgroup$ – NPSF3000 Mar 27 '15 at 2:15
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There are no "fast zombies" in Max Brooks's World War Z but the problem of zombies "piling up" is still problematic in a number of the sieges so the design question still has merit. There are two major considerations, physical strength, starting with deep foundations and continuing with continuous casting and heavy use of reinforcing steel and stopping them at the top. The basic wall is going to be an inverted uneven T with a long foundation on the outside where the weight of the zombies will act to strengthen the wall they're piling up against. The base of the wall should also be thicker than the top but there should only be a slop on the inside. I'd then use modern materials to put old-style hoardings on top in smooth steel that nothing can get purchase on.

On a separate but related note read the book it is really really good and the movie only covers a tiny slice of time (the Panic) out of the whole conflict and does it badly. Well the movie is less bad if you think of it as taking place during the Panic.

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