Though the course along the Arkansas River was selected as the cheapest and easiest route, the preliminary surveys sufficed to demonstrate that even that location would offer difficulties out of the ordinary. The 9½ miles run through the Royal Gorge, one of the natural wonders of North America, promised a heavy struggle. This defile at places is 2,700 feet deep, and the walls rise up so perpendicularly as to defy the slightest foothold to a chamois, let alone a railway. The bottom of the gulch was found to be occupied by the turbulent waters of the river, which in times of flood lapped the base of the mountain wall on either side, though at normal level a narrow shelf was exposed at the foot of one cliff. The engineer responsible for the building of the line, Mr. A. A. Robinson, decided to seize that shelf. It could be made just wide enough to carry the line and no more, while it could be raised sufficiently to escape the ravages of high water. The river was kept within bounds by a wall of rough, heavy masonry carried to a point well above the highest watermark, and on this the track was laid upon a bed of rock ballast hewn from the mountain slopes. However, when the eastern portal of the ravine was gained a serious obstacle loomed up. The ledge which the engineer had pressed into service up to this point disappeared abruptly into the water, and did not reappear for some distance beyond. The two sides of the canyon, towering up to nearly 3000 feet, come closer together, leaving only a narrow vent barely 30 feet wide. As a result the river channel is constricted, and the water thunders over the boulders through the wedge-shaped defile with the velocity of a cataract. The engineer was brought to a full-stop. How was he to span that gap? The character of the torrent absolutely prevented any possibility of sinking piers in the waterway to carry a bridge across the breach in the ledge. Nor could a path be carved out of the mountain-side to carry the line around the obstacle, because the maximum gradient had been attained already on either approach to the gap. As Mr. Robinson related, the first solution that occurred to his mind was to tunnel the shoulder, and thus to avoid the difficulty completely. But the bogey of expense stood in his way. There were scarcely sufficient funds available to build a surface line, and, under these circumstances, tunnelling was quite out of the question. Moreover, it would have required considerable time, and the public was clamouring wildly for the completion of the line. He haunted the gorge for days, and spent much midnight oil in the hope of discovering some simple, quick and cheap means of solving the problem. But the quest seemed hopeless. Then suddenly it occurred to him that, as he could not hope for assistance from the river-bed, why not force the walls of the ravine to his aid? In short, why not sling a bridge from the cliff faces on either hand?