Over some of the boldest streams it was necessary to construct suspension bridges, as they are termed, made of the tough fibres of the maguey, or of the osier of the country, which has an extraordinary degree of tenacity and strength. These osiers were woven into cables of the thickness of a man's body. The huge ropes, then stretched across the water, were conducted through rings or holes cut in immense buttresses of stone raised on the opposite banks of the river, and there secured to heavy pieces of timber. Several of these enormous cables, bound together, formed a bridge, which, covered with planks, well secured and defended by a railing of the same osier materials on the sides, afforded a safe passage for the traveller. The length of this aerial bridge, sometimes exceeding two hundred feet, caused it, confined, as it was, only at the extremities, to dip with an alarming inclination towards the centre, while the motion given to it by the passenger occasioned an oscillation still more frightful, as his eye wandered over the dark abyss of waters that foamed and tumbled many a fathom beneath. Yet these light and fragile fabrics were crossed without fear by the Peruvians, and are still retained by the Spaniards over those streams which, from the depth or impetuosity of the current, would seem impracticable for the usual modes of conveyance. The wider and more tranquil waters were crossed on balsas - a kind of raft still much used by the natives - to which sails were attached, furnishing the only instance of this higher kind of navigation among the American Indians. *43 [Footnote 43: Garcilasso, Com. Real., Parte 1, lib. 3, cap. 7. A particular account of these bridges, as they are still to be seen in different parts of Peru, may be found in Humboldt. (Vues des Cordilleres, p. 230, et seq.) The balsas are described with equal minuteness by Stevenson. Residence in America, vol. II. p. 222. et seq.] The other great road of the Incas lay through the level country between the Andes and the ocean. It was constructed in a different manner, as demanded by the nature of the ground, which was for the most part low, and much of it sandy. The causeway was raised on a high embankment of earth, and defended on either side by a parapet or wall of clay; and trees and odoriferous shrubs were planted along the margin, regaling the sense of the traveller with their perfumes, and refreshing him by their shades, so grateful under the burning sky of the tropics. In the strips of sandy waste, which occasionally intervened, where the light and volatile soil was incapable of sustaining a road, huge piles, many of them to be seen at this day, were driven into the ground to indicate the route to the traveller. *44 [Footnote 44: Cieza de Leon, Cronica, cap. 60. - Relacion del Primer Descubrimiento de la Costa y Mar del Sur, Ms.