I read through the explanations on how to set up a military, and in the new version of DF it seems that anything beyond training requires setting up burrows. I set up a burrow on the doorstep of my fortress intending to make it part of a patrol route, but as soon as I finished creating it, all the dwarves in my fortress dropped what they were doing and crammed into the 6x6 area around my floor hatches, where I had drawn the burrow. I didn't assign any dwarves to the burrow. What's going on?
Also, do burrows cover multiple z levels or just the one they're drawn on?