...pable of 150-foot spans. About 1868 iron bridges began to take the place of wooden bridges. One of the first long-span bridges was a singletrack railway bridge of 400-foot span over the Ohio at Cincinnati , which was considered to be a great achievement in 1870. The Kinzua viaduct, 310 feet high and over half a mile long, belongs to this era. It is the type of the numerous high viaducts now so comm...