HISTORY OF BRIDGES.
The construction of perfect bridges, being a very complex operation, cannot have taken place amongst a rude and uninformed people ; and in the course of this discussion it will be seen, that this did not always corres pond with the progress of the other arts, even in situa tions where the intercourse was great.
The most obvious and simple bridge is that formed by single trees thrown across small streams, or, in case of broader streams, by fastening the roots of a tree on each bank, and twisting together their branches in the middle of the stream. These must have frequently occurred by chance, and they fall within the compre hension of the hunter ; accordingly Mr Park found even the latter mode practised on rivers in the interior of Africa.
The next step is not much more complex, for in a space too great for the beforementioned operations, few manual arts were required to form ropes of rushes or leathern thongs, to stretch as many of them as were necessary between trees or posts on the opposite banks, and connect and cover them so as to form a slight bridge The following accounts, given by Don Antonio de Ulloa, will afford a distinct notion how these sorts of bridges were constructed and used in the mountainous parts of South America. See vol. ii. page 164. London, 4th edit. Svo.
"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 cur rent, 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 that country, and called by the Indians, Ichu ; and these cables were the foundation of the whole structure. Two of these being laid across the water, fascines of dry juncia and tortora, species of rushes, were fastened together, and laid across them. On these the two other cables were laid, and again covered with the other fascines securely fas tened, 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 to 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 that Ynca, and since often confirmed by the kings of Spain, on account of its prodigious use ; it being the channel of intercourse between those provinces separated by the Desagua dero."
Again, in vol. i. page 430 : "When the rivers are too deep to be forded, bridges are made at the most fre quented places. Of these there are two kinds besides those made of stone, which are very few : the former of wood, which are most common ; and the latter of buju cos. With regard to the first, they choose a place where the river is very narro)v, and has on each side high rocks. They consist of only four long beams laid close together over the precipice, and form a path about a yard and a half in breadth, being just sufficient for a man to pass over on horse-back ; and custom has rendered these bridges so natural to them, that they pass them without any apprehension. The second, or those formed of bujucos, are only used where the breadth of the river will not admit of any beams to be laid across. In the construction of these, several bujuros are twisted together, so as to form a kind of large cable of the length required. Six of these arc carried from one side of the rivet to the other, two of which are con siderably higher than the other four. On the latter are laid sticks in a transverse direction, and over these branches of trees as a flooring ; the former are fasten ed to the four which form the hridge,and by that means serve as rails for the security of the passenger, who would otherwise be in no small danger from the con tinual oscillation. The bujuco bridges in this country are only for men, the mules swim over the rivers ; in order to which, when their loading is taken off, they are drove into the water near half a league above the bridge, that they may reach the opposite shore near it, the rapi dity of the stream carrying them so great a distance. In the mean time, the Indians over the loading on their shoulders. On some rivers of Peru there are bujuco bridges so large, that droves of loaded mules pass over them ; particularly the river Apurimac, which is the thoroughfare of all the commerce carried on be tween Limb, Cusco, La Plata, and other parts to the southward.