Mostly circular to work dumb units around the outside instead of trying to get into the base. Traps for earthbound guys set inside the wall where they're more effective. Air defense sacrininjad a bit cause most people don't bring dragons to try to loot off of you. Stores separated and isolated to limit your loot being stolen when you are effectively attacked. Dark elixir hard to get to. Wizards inside where they can zap the goblins that try to steal your loot.