New guy interested in military fortifications specifically made of DIRT

[Lykos]

So an odd inquiry i know however from what i've seen they are pretty cool. Specifically i would like more information on how trenches are built used and maintained, bunkers, and dirt walls. I have always loved Architecture and Engineering, right now I am running a game called Dungeons and Dragons you might have heard of it. So naturally knowing more about how things are built can lead to building more awesome things so if you didn't have to really worry about logistics or labor costs what sort of amazing things would you make? Right now the world my players are on has no metals, so you know everything is pretty much dirt, stone, wood, or bone. With these resources what would you expect them to build? How would they fortify positions? How would they handle irrigation of crops? I pretty much have their military tech worked out but i'm trying to figure out architecture. Don't think that just because they are low tech means that they are dumb by any means assume that their engineers and architects are just as smart as you or me, so go nuts and have fun.

Also thank you in advance for any help you can give me.

[RWOLFEJR]

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The three little pigs vs. big the bad wolf... The first book on construction for most of the U.S. population far as I know. The three pigs had the best results with their brick house... stones and mud.