Of Bridges, as Roads.-A road is as much an artificial work as a house or a bridge: indeed, a bridge is only a road across such a chasm as cannot be passed without one. There are, indeed, two uses of a bridge; the first to pass over, the second to pass under: the first is always necessary, the second only occasionally so, as where the water under it is navigable: yet, self-evident as this fact may appear, bridges are often raised so high as to make the passage over them difficult and dangerous, when no passage under them is required; and, perhaps, a form of bridge, adapted to the purposes of passing over, which may unite strength with grace, or use with beauty, is a desideratum in architecture; for this purpose I have suggested, for several places, what may more properly be called a viaduct than a bridge, of which no idea can be given by description only.
