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My story requires humans very quickly creating a ~5km barricade to protect them from the monsters that live in the forest. These monsters are between animals and humans in power/intellect.

Currently, I thought of cutting down every X tree along the natural tree perimeter, then attach that tree sideways to the standing trees. Basically using uncut trees as the posts.

But my brother brought up a trench, which seems like more work, and more/less secure. Some animals can jump pretty far, and/or climb. To make the trench tall and wide enough would be very laborious.

So I'm curious what other low-cost ways to create a barricade would be.

Requirements:

  • The humans are resource poor, starting from scratch (wood/stone), but they do have numbers and stamina.
  • The barricade should keep out large and small animals. Flying ones get past.
  • Must be fast to set up, within a week, including overnights if necessary.

// ANSWER //

After reading all your suggestions, a trench sounds the most feasible for my scenario. The roman factoid gives me confidence in this idea. I forgot to mention it's on an island, so they can't run away, and the humans were there first for a decade or so, so they have some infrastructure. Burning down the forest does sound like a good idea, but I imagine the soot would kill the humans, and possibly the food sources too.

In sum, I may use a combination of these suggestions as the crude methods buy more time for something better.

Thanks everyone!

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  • $\begingroup$ Some powerful magician? Is your world magic or is it not? $\endgroup$ – Peter M. Dec 16 '14 at 14:36
  • $\begingroup$ How strong and intelligent are your monsters? If they are dangerous enough to threaten the humans, won't they be capable of breaking down / climbing over simple wooden walls? Also consider that chimpanzees are capable of simple tool use, so if they are more intelligent than animals, they must be more difficult to contain than chimpanzees at the very least. $\endgroup$ – March Ho Dec 16 '14 at 14:38
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    $\begingroup$ You might consider re-titling this question. From the outside, I thought you were asking about electromagnetic sci-fi shielding configurations... $\endgroup$ – Telastyn Dec 16 '14 at 15:01
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    $\begingroup$ Quick barricade against monsters in the forest??? BURN THE FOREST!!! The fire will probably burn for days, killing most of them and providing a nice wall of flame - and afterwards you will have a nice flat land where you see em coming from afar! $\endgroup$ – Falco Dec 16 '14 at 15:57
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    $\begingroup$ Abatis from trees (cut in V shape to overlap) provide substantially better protection than burned forest $\endgroup$ – Peter M. Dec 16 '14 at 22:59
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That's what the Romans did. They dug a pit/trench all the way around the camp, leaving 'gated' areas at the ends to get in and out. when they dug the trench they threw the dirt into a pile on the inside, making a trench down and then a hill back up which the attackers would have to travel. Giving them the high ground and making it easier to defend. On top of that the more impending the danger needing defense they would also line the trench and facing hill with sharpened stakes to slow the advance down even more. Using caltrops in the open spaces in front will slow a charge but this was for more imminent attacks. The longer they were in an area the more open space they would clear to more easily spot an enemy approaching.

But I believe that the Roman legions did this at least the trench/hill every night they were on the march especially if camping in the open.

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    $\begingroup$ When Caesar wanted to block the Helvetii from marching through Provence, he asked for 2 weeks to deliberate and had his men build a 18 mile long, 16 foot high with a trench in front in that period. He did this with 1 legion working. $\endgroup$ – Oldcat Dec 16 '14 at 18:22
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    $\begingroup$ @Oldcat Yes the legions could move mountains. $\endgroup$ – bowlturner Dec 16 '14 at 18:26
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How many humans to hold down your 5km border?

Low-tech? You're pretty much screwed, especially if there's a numerical superiority of attackers (3-to-1), or if you're spreading your defenders out (ie: attackers can put together a disproportionate force at one point vs. defenders at that point). The larger the border you try to hold down, the more dispersed your defenders are. If you're leaving one guy holding down 50' of border - it'll only take 3-4 human equivalent attackers (minus however effective your barrier is) to overwhelm him, and pierce your defenses, then roll up the flanks of your other defenders. If you can see them coming (low-tech means you're screwed for night attacks), and can move quickly, you can have your defenders grouped up but spread out a bit more (well, not a lot more than 100'), so they can come to each other's aid. Beware of feints to draw in surrounding defenders leaving holes in your defenses. The larger your defending group, the bigger the attacking group will need to be. Also, figure in your advantage in ranged weapons and armor. Unless your monsters are pretty tough.

If you want it realistic, have your humans move somewhere with better defenses. An island, a peninsula, or land between two rivers, or as Pavel suggests, a cave. Or build a castle (and pack in the defenders).

A barricade isn't going to be effective against anything that can climb, dig or leap (for reasonable barriers - if you can build them 20' high and make them smooth - maybe you've got a chance). Most predators are going to be capable of scaling 10' and 12' fences. I've seen coyotes jump over 8-10' fences. Once you start trying to build fences higher than 10', especially of anything substantial, you're going to have to start building scaffolding and putting it up and taking it down. Block and tackle rigs, etc. That's not going to be fast. Heck, logging your forest isn't going to be fast either (without chainsaws, steam-donkeys or bulldozers/tractors). Nor is evening up your trees, so you don't leave climbable outsides, or chinks inbetween them. You're going to have to drag your trees from further in the forest to your perimeter line. At around a 1' in diameter, figure you're going to have 20 to 40' lengths, and need ~12 per 10' in height (trees aren't parallel). ~5468 trees you're going to need to cut down for a 10' high fence. ~20m for an experienced ax-man per tree, assuming nice iron/steel axes are available - stone axes means a ridiculous amount of time more. How many axes do you have? Sharpening stones for each ax? New ax handles for the inevitable breakage? Around 30m to an hour for an unskilled worker. After which they're going to have sore hands, be winded, and the next one will take longer. You're also going to max out at somewhere around 6-12 hrs of (useful) work per day, of heavy manual labor, for unskilled people. You've still got to lop the limbs off, and drag it to your fence line, and/or lift it into position. How're you attaching these trees? I hope you've got a lot of rope. It might be possible to get many trees that're close enough that you can wedge them between alternating trunks. That will take a fair amount of surveying and planning. Btw, the number of trees given is for a perfectly straight 5km - if you vary your line at all (in order to use existing trees as uprights for example), it's probably not going to be straight - so be sure to add more work. You could also use some felled trees as posts, and dig out a nice hole near one upright tree and put a post in, keeping your horizontals inbetween the two. Still going to need a fair bit of rope to be putting up each section. If you don't have that much heavy duty rope / chain available, you're only going to be able to put up each section one at at time. You've got 546 sections to do. Let's WAG it at 10 hours for a 10' section (even higher gets an even longer time) - that's 227.5 days if you've only got one rope-set. You'd be better off spending some of your time making rope / chains for starters if you don't have enough.

Also, remember that logging, especially old-school logging, is one of the most deadly professions. And even more-so for amateurs and for people who're working under stress; tired and fearful. They tend to make even more mistakes. Expect to kill a number of people in putting up these defenses.

Old school trenching (shovels, etc) is even more labor intensive, backbreaking, and not very effective at keeping animals that can climb / leap out. It'll work on horse-like monsters. But not so great at anything else.

If you've got the proper tools and horses, you can make some stuff which will move ground faster than shoveling. Might be worth your time to spend it building that equipment, then get working on trenching. But that's also going to be determined by your soil. Got clay? Some clay is next to immovable. As is bedrock. They even have trouble dynamiting that clay out here. It just laughs at jack-hammers. I can only imagine trying to go after it with a pick and shovel.

Are your monsters afraid of water? Would a moat work? Redirecting water to cut a trench would be much more effective, especially if you've got height differential to work with. You only have to survey and cut a nice starter trench, then start dumping the water through. 5km may be a little long to expect the height differential to continue working, however. I know you can easily get 500' to clear with a reasonable head of water.

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  • $\begingroup$ You have some good points, but I stopped trusting your estimates when you said "I've seen coyotes jump over 8-10' fences." Because, no, no you didn't. $\endgroup$ – Samuel Dec 16 '14 at 17:13
  • $\begingroup$ @Samuel no coyotes nearby, but it wouldn't be totally implausible - e.g. news.terra.com/… ; and zoo fence heights assume that the fences aren't climbable (the OP proposed wooden wall would be) and that there aren't large climbable objects nearby, which again would be an issue for a 5km wall over rough unprepared terrain. $\endgroup$ – Peteris Dec 16 '14 at 18:27
  • $\begingroup$ @Samuel OK, zoo guidelines such as epa.govt.nz/Documents/… do require only ~8' for such animals, so they most likely can't jump over 10'. Still, both the originally proposed wall and trench would be climbable and thus not an obstacle for many kinds of animals. $\endgroup$ – Peteris Dec 16 '14 at 18:34
  • $\begingroup$ @Peteris Uhhh, that's a 9-foot tiger jumping a 12-foot fence. A coyote is like a medium sized dog; 2.5-feet from head to rump. And user3082 said the Coyote jumped over a fence, not scrambled up it. My point remains. $\endgroup$ – Samuel Dec 16 '14 at 18:39
  • $\begingroup$ Samuel, yes I did. I did a double-take because at first I thought it was a dog (and I've never seen a dog jump a fence that high). I then went and measured the fence. Regular block fence, the ground around the fence varied in height versus the top of the fence - so it could've been the lesser of those two values. I was at a distance of ~150' away (I didn't measure my observation distance - but I easily could, that location is on my daily travel route). $\endgroup$ – user3082 Dec 24 '14 at 8:55
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a ~5km barricade

I'm assuming you mean a circumference of about 5km (not 5km tall!)

they do have numbers and stamina

It matters exactly how large their numbers are. Suppose you have 5000 people. They can all link hands and spread out into a big circle with each person about 1m apart and you then have your 5km perimeter. Each person only needs to deal with a 1m defensive line in that case, either by digging a trench or erecting a wall.

The humans are resource poor, starting from scratch (wood/stone)

If you want a wall made of stone, you need to have a pre-existing stockpile of stone & mortar etc, or your people are going to have to mine it, which they can only do if they already have decent picks, hammers and other stoneworking tooks. I'm taking it from this statement that your people don't even have the resources to begin a quarry so this is ruled out.

If you want a wall made of wood, you also need a pre-existing stockpile of logs, unless your humans are going to go logging in the exact same forest they're trying to stay away from because it's full of monsters. Unless they already have the weapons to defend themselves on these sorties (which would undermine their motivation for running away anyway) as well as the axes, ropes etc necessary for a productive logging mission, this is also a no-go.

A trench, on the other hand, can be built immediately with your bare hands. Obviously a shovel makes things a lot easier but it seems like your people are desperately struggling for survival so they'll hunker down for a few days scooping dirt if that's what they have to do to be safe. If they have a water supply to turn it into a moat that could make it more effective (some animals would jump a dry trench but not risk drowning if the same trench is full of water). Water will also make it seem a more formidable defence even if it's not that deep. The disadvantage is that the sides may collapse and turn it into a smooth depression in the ground which can be walked in and out of easily.

However, you also said this:

monsters that live in the forest

which makes me think the most efficient defence for them would be simply to migrate away from any forests/cause massive deforestation in whichever area they choose to settle in by burning the whole thing down. Once they're living on the (newly fertilised) land near to recently destroyed forests, they can send their bravest defenders forth to set fire to other forests nearby and keep fighting back against the monsters' habitat.

Eventually a few thousand years will have passed and the humans will start feeling concerned over the endangered species whose habitats they've destroyed, having completely forgotten that they used to be such terrifying deadly monsters. Kinda like real life, actually.

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  • $\begingroup$ When I first read the question, I thought it meant 5km tall... $\endgroup$ – KSmarts Dec 23 '14 at 20:34
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Abatis - you can do it by cutting trees in certain pattern, and leaving them in place. No digging. Abatis substantially slows attackers, and they provide some protection for defenders.

abatis image

But you will have hard time to protect 5km defense line - you will need thousands of defenders. Better off, use some naturally protected cliff, and build defensive trench on narrow area where approach is possible: Hill fort

BTW, cutting trees for such abatis is much faster than digging trench and building a barricade. Con is that abatis slows also movement of your own forces. Any engineering is like that - it is all about compromises.

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  • $\begingroup$ Most trees have gaps between them wide enough to allow creatures through. $\endgroup$ – user3082 Dec 16 '14 at 17:09
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    $\begingroup$ That's why you cut them down in overlapping V pattern. Scroll down for the image. $\endgroup$ – Peter M. Dec 16 '14 at 17:11
  • $\begingroup$ Ahh, so not really a barrier - just something to slow down your attackers. Meaning you've still got to maintain an active defensive watch. $\endgroup$ – user3082 Dec 16 '14 at 17:13
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    $\begingroup$ But of course you need to keep watch - even city walls can be scaled or undermined. $\endgroup$ – Peter M. Dec 16 '14 at 17:15
  • $\begingroup$ Some, but he's not defined 'monster' at all. If it's just an animal, if you've got a nice enough wall they'll just continue on their way somewhere else, unless the smell or something else is utterly enticing. Anything that's not specialized for digging, and not intelligent won't undermine a wall just to get in - although might dig to escape an enclosure. $\endgroup$ – user3082 Dec 25 '14 at 9:47
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This is one of reasons why humanity started from cave: What keeps them at this specific location? It ain't get better in other place, because monsters are everywhere.

Yes, true, but it does not hold you back to go uphills. Go to cave, where you have to defend only small place (entrance to the cave) and it evens out the numbers pretty fast.

So, other tactics could simply be: Find easy to defend place

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  • $\begingroup$ That's legend. Cavemen did NOT live mostly in caves. The cave was far from being the primary residence. Caves are easier to excavate, and protect artifacts better. $\endgroup$ – Peter M. Dec 16 '14 at 16:58

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