R. Yoshiyah says (Numbers 11:31) "And He spread them over the camp": three parasangs on each side. And what is the intent of (Ibid.) "about a day's journey on this side and a day's journey on that side"? In height. Three by three, making nine (parasangs on each side). Nine and nine, eighteen (all together.) (And thus on all the sides roundabout the camp, as it is written) (Ibid.) "and about two cubits deep on the ground" (roundabout the camp.) And it is written "And He made them fall in the midst of the camp around their dwellings."