On this section the engineers accomplished an unparalleled engineering feat. The narrow Isonzo gorge had to be crossed, and it was effected by throwing a single span from one bank to the other, a matter of 733 feet. This is the longest single-arch masonry bridge in the world, and the rail-level is 120 feet above the level of the water. As the coast is approached the windings of the line become more tortuous, while the bridging, owing to the numerous rivers, is terrific. When at last Opcina tunnel is penetrated, the Adriatic is seen spread out in a vast panorama 1000 feet below. To descend the mountain slopes with an easy grade for a distance of ten miles was a stiff problem. In order to do so the engineers had to carry the track in the form of elaborate saw-like loops. Heavy gradients could not be avoided, and this part of the line is one of the steepest and most trying to the locomotives. Though these sections of the railway had proved difficult to carry out, it was the Tauern link in the chain that tried the energy and ingenuity of the engineers to the supreme degree, for on this stretch of railway the mighty Tauern group of mountains had to be negotiated. Surveys showed that to pierce this clump involved the boring of a tunnel for a distance of five miles at least. They proved the hardest five miles in the whole undertaking; the piercing of the Karawanken and Wochenier tunnels sank into insignificance by comparison, for this knot of the Alps was found to be formed of much sterner rock. Granite gneiss, one of the hardest substances against which it is possible to bring the edge of a drill, made progress provokingly slow. At times, when the hand drills had to be used, an advance of two feet in the course of twenty-four hours was considered excellent. The Brandt hydraulic drills, however, with the enormous energy behind them, made the task somewhat lighter, for they moved through the hardest rock at a rate of about seventeen feet every day, with occasional spurts of a foot per hour. In this undertaking, however, many misfortunes served to delay progress. The task had barely commenced, when a flood destroyed part of the works at the northern end. The river whose water had been harnessed had been deviated from its accustomed path, because it flowed over the roof of the tunnel. As the engineers had no desire to invite an inundation by tapping the bed of the river waterway, they had provided it with a new channel. Heavy snows and rains, however, so swelled the volume of the diverted river that it broke through its artificial bonds to resume its original course. The result was that, owing to the crust of earth between the old bed and the roof of the tunnel being so thin, the water crashed through, and poured into the tunnel in an immense cascade.