Chapter 15

I'm not exactly sure what you are asking but hopefully this quote from chapter 15 helps:

"They were four days gone, and by that time they knew that the joined armies of the Lake-men and the Elves were hurrying towards the Mountain. But now their hopes were higher; for they had food for some weeks with care-chiefly cram, of course, and they were very tired of it; but cram is much better than nothing-and already the gate was blocked with a wall of squared stones laid dry, but very thick and high across the opening. There were holes in the wall through which they could see (or shoot) but no entrance. They climbed in or out with ladders, and hauled stuff up with ropes. For the issuing of the stream they had contrived a small low arch under the new wall; but near the entrance they had so altered the narrow bed that a wide pool stretched from the mountain-wall to the head of the fall over which the stream went towards Dale. Approach to the Gate was now only possible, without swimming, along a narrow ledge of the cliff, to the right as one looked outwards from the wall. The ponies they had brought only to the head of the steps above the old bridge, and unloading them there had bidden them return to their masters and sent them back riderless to the South. There came a night when suddenly there were many lights as of fires and torches away south in Dale before them."