I have lingered over Auhsien Suspension Bridge not because of its craftsmanship, but because it marks a primitive phase in the evolution of metal bridges. Perhaps the example seen by Kircher was less rude; and perhaps the principle of its construction may have been precisely like that in the bamboo swing bridges of Western China. In these there are four huge cables of twisted bamboo[142]: two of them carry the footway, while the upper ones serve a double purpose: a strong netting on each side braces them to the lower cables, giving another support to the footway, and forming a sort of hammock a good deal taller than an average man. It is within this deep hammock that everybody walks across a bamboo swing bridge, which in a high wind is as enjoyable as a rowing-boat. At each abutment there is a gabled entrance gate, where the four cables are screwed up.[143] Displace the bamboo cables for iron chains, and we get at once, perhaps, an idea of the bridge that Kircher regarded as “merveilleux.” As Kircher’s book was published in 1670, an iron bridge ought to have been built in Europe before the middle of the eighteenth century. An attempt to build one was made in 1755 at Lyons, but it failed. An arch was put together in a builder’s yard and then the project was abandoned as too costly! But the idea was handed on somehow to an English ironmaster, Abraham Darby, of Coalbrookdale, who in 1779 won a great success by bridging the Severn with a very useful arch of cast-iron, having a rise of 50 feet, and a span of 100 ft. 6 ins. The cost of it is not known, but the weight of metal employed was 378½ tons. The design is bold, and the arch handsome. Every pontist should get a photograph of Coalbrookdale Bridge. Already it is out of date, and its value as history will not save it from destruction. A few years later, in 1796, Rowland Burdon followed the example set by Abraham Darby, but not as a mere copyist, his Wearmouth Bridge being an arch of open cast-iron panels, which act as voussoirs. The span is 236 feet, with a rise of 34 feet; the springings are 95 feet above the river-bed; at first the footway was rather narrow, but in 1858 it was widened by Robert Stephenson. Rowland Burdon used 260 tons of iron, and his work cost only £27,000.