This, as I heard before, could be let fall in a moment, so as to crush a score of men, and bar the approach of horses.

Behind this tree, the rocky mouth was spanned, as by a gallery with brushwood and piled timber, all upon a ledge of stone, where thirty men might lurk unseen, and fire at any invader.

From that rampart it would be impossible to dislodge them, because the rock fell sheer below them twenty feet, or it may be more; while overhead it towered three hundred, and so jutted over that nothing could be cast upon them; even if a man could climb the height.

And the access to this portcullis place--if I may so call it, being no portcullis there--was through certain rocky chambers known to the tenants only.
But the cleverest of their devices, and the most puzzling to an enemy, was that, instead of one mouth only, there were three to choose from, with nothing to betoken which was the proper access; all being pretty much alike, and all unfenced and yawning.

And the common rumour was that in times of any danger, when any force was known to be on muster in their neighbourhood, they changed their entrance every day, and diverted the other two, by means of sliding doors to the chasms and dark abysses.
Now I could see those three rough arches, jagged, black, and terrible; and I knew that only one of them could lead me to the valley; neither gave the river now any further guidance; but dived underground with a sullen roar, where it met the cross-bar of the mountain.