Classifications of bridges are done according several criteria. One is according the form: slab, arch, cable, beam or truss bridge. Next criteria is related to the materials used in the construction and they can be made of timber, steel, stone or concrete. Bridges are different according to the location, the length, the function and the inter-span relationship. Also before drawing and building one, there are lengthily researches about the best materials, the expenses, the terrain and the purpose of the bridge.