Viaducts are types of bridges; the term “viaduct” refers to long bridges or series of bridges that are connected to one another or structurally supported by arches or sturdy platforms between two end towers. As with bridges, viaducts may cross waterways or roadways, and exist primarily to provide an overhead passage to move trucks, cars, trains and pedestrians from one point to another.
Viaducts belong to the larger class of modern-day bridges, but bear a remarkable resemblance to the aqueducts constructed and used by ancient Romans. Roman engineers and architects created aqueducts initially for the purpose of transporting water through cities and from cities to residents outside city boundaries. Aqueducts proved to be sturdy and reliable structures, requiring little maintenance and capable of holding large amounts of weight. For that reason, their use expanded to include transportation as well. Roman aqueducts looked similar to those of more modern design. They existed as long spans that were supported on both ends by solid arch structures attached to stones, masonry or piers. The design of the Roman aqueduct remained in use until the late 18th century, when bridges began to be formed from iron, and in the 19th century by steel. Although the design remained the same, aqueducts in the 20th century were made primarily from concrete.