Out of all buildings, plain old walls are surprisingly complicated. You get about a hundred of them. 100 walls? What? It turns out a “wall” is just a tiny block. Making what a human would describe as a wall involves dragging dozens of them into a line.
There are short-cuts, glitchy ones. Selecting an entire row might also get you the corners, or not, and probably stops at walls of a different upgrade level. Dragging a whole row into a smaller space won’t work – you’ll need to unselect, trim to the correct length, then reselect. There’s an etch-a-sketch mode — trace on squares to place walls, and/or select the tiny handles and pull out a line of walls. It’s still not easy, but better than dragging 100 of them by hand.
Once you figure out how to place them, where you’re putting your walls is all wrong. Everyone starts with a rectangle around everything. That’s no good — the enemy only needs to poke a single hole. Some people make a double-thick inner keep. Also no good — the game has special rules making it not work: wall-blasters have a radius of 2. It turns out that a series of boxes, with shared off-center corners, is the best. It looks like garbage, but it works great.
If you get really into it, there’s exact math as to how much extra distance a wall counts as. You can fine-tune your base so attacking troops tend to go in odd directions or split up.
Finally, walls are a cash-sink for hard-core players. They’re the only building that takes 0 time to upgrade. If you want to play all day, upgrading walls is the one thing you can do. It’s not cheap, and you have 200 of them, so you’ll always be able to “work on your walls”. It has this funny quirk: even though it takes no time, you still need a free builder. So, regular players can put all 5 builders to work. They can’t upgrade walls while they wait, which is fine. Meanwhile, hard-core players need to leave one free so they have it to wall-upgrade through-out the day. That seems fair, sort of.
The coolest thing about walls is something just for looks. If walls actually filled their squares, they’d look terrible. They look better filling about half — like thick poles. But that means adjacent walls would have spaces between them. They fix that by auto-creating a special wall-connector segment. It doesn’t look great.