Before the principle of lofty iron piers had been thoroughly developed, many high piers had been built of timber both at home and abroad. More particularly was this the case in the United States of America, where the presence of magnificent timber close to hand offered special inducements for the use of wood. Like a mammoth scaffolding, each pier was constructed with a most liberal supply of material, judiciously selected and carefully put together, but the danger of destruction by fire was ever present from the beginning. Probably more timber piers and bridges have been destroyed by fire than have been removed on account of natural decay. One of the most notable of these timber-pier constructions was that of the Old Portage Viaduct, on the Erie Railway, U.S.A. Fig. 101 is a sketch of one or two of the piers. This viaduct was more than 800 feet long, and 234 feet high from the bed of the river to the rail-level. The spans were 50 feet each. Masonry piers were carried up to about 25 feet above the ordinary water-level of the river, and upon these the timber superstructure was erected. Each timber pier consisted of three complete sets of framework, securely connected together, and also well stayed and braced to the adjoining piers. This viaduct was destroyed by fire in 1875, and was reconstructed with piers and girders of iron. Railway bridges over or under public roads of primary or secondary importance must be constructed to the widths and heights prescribed for such works in the fixed regulations of the country in which they 103 have to be built. As a rule, these road-bridges are simple and inexpensive in character, except in towns, or in cases where the line crosses the roads very obliquely, or where the road is situated at the top of a deep cutting, or bottom of a high embankment. Away from towns and out in the open country, permission is generally obtained to divert the roads to a moderate extent, so as to obtain a more favourable angle and height for the bridge; but in towns, where the roads become streets, sometimes of great width, with houses and shops on each side, little or no diversion can be allowed.