Bridges connect and bridge something. A river, canal, gorge or valley, road, railway or other challenge. A bridge design can carry a railway, roadway, canal or water main. We also call a long bridge a viaduct. Usually large bridges are made of reinforced concrete, masonry, steel or cast iron. The superstructure of a bridge is over which traffic passes and the substructure has pillars, foundations that transfer the forces of the bridge to the subsurface. Below is a selection of the available aerial photos of bridges. More available aerial photos showing bridges can be found by searching the image bank.