VII
PRIMITIVE SUSPENSION BRIDGES
Wehave seen (p.114) that the first suspension bridges were of two sorts: (a) long branches which had grown across rivulets and chasms; (b) thick and tough creeping plants by which many forest trees were festooned to one another. It is a vast evolution from these natural things to the art of Ulric Grubenmann, the forerunner of metal suspension bridges.[52]Unfortunately it is also an evolution which we cannot follow through many consecutive phases, artists and historians having failed to record its growth. We cannot suppose that theancients neglected suspension bridges; from the spider alone they must have learnt that pendent ropes made a good bridge; but we know not what they achieved in this airy handicraft. Many people of to-day show in primitive hammock-bridges that their ancestors were influenced by the work of spiders. In countries so far apart as China and Central Africa and Northern India, for example, there are hammock-bridges of cane and osier, netted elaborately at the sides and swung by bamboo cables, as in China, or by ropes made from the silky fibres of the Nilgiri nettle, as in the Bermulda Hills. Whatever sort of primitive rope is employed, its first model was the gnarled and twisted stem of a vine-like creeping plant.
Perhaps the most ancient suspension bridge in China is the one known asLiu SohorLew saw, literally a slip rope. A bamboo cable is fixed from side to side of a ravine, not in a level line, but a little aslant, so as to form a mild sort of switchback. A traveller carries a wooden saddle with a deep groove in it; the groove fits the bamboo cable, and straps fasten the saddle and give confidence to the jockey, who travels at a rapid speed when he is fat. On his return journey he is pulled up the bridge by ropes. In the mountains of Sichuan there are hundreds of these single cable-bridges.[53]What are they but lianes and vine stemsplusa little human primitiveness?
Don Antonio de Ulloa, the Spanish Admiral, describesa Peruvian bridge closely allied to the Chinese Liu Soh, and called the tarabita. Ulloa noticed it on several rivers, but particularly on the rapid Alchipichi. The tarabita is only a single rope made of bujuco, or ox-hide thongs twisted into a cable from six to eight inches in thickness. It is extended from one side of the river to the other, and anchored firmly. On one bankside it is controlled by a wheel, or winch, that makes it either taut or slack. A leather cradle is hung from the tarabita by two clasps that have rounded heads; two ropes are stretched across the river and bound to the travelling clasps; a wayfarer sits in the cradle and is pulled across by the guide-ropes. Even mules are slung from two tarabitas, according to Antonio de Ulloa, whose book on South America was published in 1748, at Madrid. An English translation appeared in 1758, and ran into five editions. Let me give a quotation from the fourth, issued in 1806. It concerns a venerable suspension bridge akin to the bamboo variety made in the mountains of Sichuan inChina:—
“Over the river Desaguadero is still remaining the bridge of rushes invented by Capac Yupanqui, the fifth Ynca, for transporting his army to the other side, in order to conquer the provinces of Collasuyo. The Desaguadero is here between eighty and a hundred yards in breadth, flowing with a very impetuous current under a smooth, and, as it were, a sleeping surface. The Ynca, to overcome this difficulty, ordered four very large cables to be made of a kind of grass which covers the lofty heaths and mountains of thatcountry, and called Ichu by the Indians; and these cables were the foundation of the whole structure. Two of them being laid across the water, fascines of dry juncia and totora, species of rushes, were fastened together, and laid across them. On these the two other cables were laid, and covered with the other fascines securely fixed, but smaller than the first, and arranged in such a manner as to form a level surface; and by this means he procured a safe passage for his army. This bridge, which is about five yards in breadth, and one and a half above the surface of the water, is carefully repaired or rebuilt every six months, by the neighbouring provinces, in pursuance of a law made by the Ynca (Capac Yupanqui), and often since confirmed by the kings ofSpain.”[54]
“Over the river Desaguadero is still remaining the bridge of rushes invented by Capac Yupanqui, the fifth Ynca, for transporting his army to the other side, in order to conquer the provinces of Collasuyo. The Desaguadero is here between eighty and a hundred yards in breadth, flowing with a very impetuous current under a smooth, and, as it were, a sleeping surface. The Ynca, to overcome this difficulty, ordered four very large cables to be made of a kind of grass which covers the lofty heaths and mountains of thatcountry, and called Ichu by the Indians; and these cables were the foundation of the whole structure. Two of them being laid across the water, fascines of dry juncia and totora, species of rushes, were fastened together, and laid across them. On these the two other cables were laid, and covered with the other fascines securely fixed, but smaller than the first, and arranged in such a manner as to form a level surface; and by this means he procured a safe passage for his army. This bridge, which is about five yards in breadth, and one and a half above the surface of the water, is carefully repaired or rebuilt every six months, by the neighbouring provinces, in pursuance of a law made by the Ynca (Capac Yupanqui), and often since confirmed by the kings ofSpain.”[54]
In the first volume of his book,chap.VII., Antonio de Ulloa visits the Andes, and finds there some tree-bridges, some stone bridges, and some complex bujuco bridges. The stone variety he does not describe, but he writes interestingly about the bujucos. When six cables have been made by twisting together strips of ox-hide they are suspended across a river, not in a single row, but in two tiers, the lower one with four cables, the upper with two. Over the lower tier branches and canes are laid transversely; and when this floor is braced to the upper cables, there is a sort of cage within which travellers can walk in safety while the bridge swings.
“On some rivers of Peru,” says Ulloa, “there are bujuco bridges so large that droves of loaded mules pass over them; particularly over the river Apurimac, which is the thoroughfare of all the commerce carried on between Lima, Cusco, La Plata, and other parts to the southward.” Humboldt passed over one of these pendulous bridges, and Miers crossed another which was strong enough to bear the traffic of pack-mules, though it was two hundred and twenty-five feet in span.
And now we must pass on to a half-suspension bridge which is very common among the N’Komis, a tribe that inhabits the Fernan Vaz district in Equatorial Central Africa. It is a bridge built withY-shaped sticks. Two parallel rows of these pronged branches are driven into the bed of a stream, and into the banksides; then long runners are put between the forks to bear a footway of sticks laid across them transversely.
Mr. Thomas Beddoes, an African trader, and traveller, draws my attention to this bridge of forked branches; and tells me also that in the Agowe district, but far inland from the banks of this river, he came upon a primitive suspension bridge partly made with very thick vines—vines as thick as a man’s leg—which were joined together into a couple of natural ropes long enough to be suspended from trees over a creek about two hundred feet wide. Perhaps a yard separated them, and they were parallel to each other. When anchored to the trees at a height of four or five feet above the bank, they form the upper part or parapet of thebridge. As for the footway, its bearers were saplings—young trees from ten to twelve feet long and three or four inches in diameter; they were lashed together into a continuous runner, and two such runners were laid from the banksides over the creek, to carry a hurdle pathway of canes or sticks. Then the upper part of the bridge was braced to the saplings with thin vines, which were tied to their supports at intervals of about a foot, and which served the purpose of suspension rods, for they counteracted the strain on the saplings when a native crossed the narrow footway.
It would be easy to write much more about primitive swing bridges, but enough has been said to stimulate thought and discussion. Not one of them has a brighter intelligence than that which we find in many prehistoric handicrafts.