To stand the ladders against the wall may or may not be the end of a siege. To lay a siege means to surround and begin a long attack against something.
One can lay a trap and lay a bet, I assume that a general can lay a siege. I wonder how the language handled this when sieges were in vogue. I can see how (consider - go to hospital and go to university) the "a" could be taken out from BrE, but what was used in the past? Also, is it "lays siege to" or, "lay siege to"?