Although the first engineer to design a beam, or "girder," bridge is not known, some of the earliest examples have been found in East Asia and South America. These were often made using natural fiber ropes and vines.
Even earlier examples probably made use of stone slabs or tree trunks laid across a waterway.
Roman beam bridges were constructed using wooden supports and heavier duty construction materials. With the Industrial Revolution, wrought iron became popular as a stronger, more tensile material.
The simple construction of beam bridges has assured their continued use over time. Nowadays there are two main types — metal and reinforced concrete — which are used to span distances of up to 250 feet.
Often road bridges will use both concrete and steel beams, as a means of withstanding heavy pressure over time.
Engineers design beam bridges so that the top layer dissipates compression to the bottom layer in the form of horizontal tension, which is then carried by the vertical columns. To span greater distances, these vertical columns need to be heightened proportionally with the lengthening of the beam. This necessitates additional supports between the columns and beam in the form of trusses.