The term bridge is used to designate those constructions that serve to connect different spaces that otherwise could not be accessed. Through the ages, the design and engineering of bridges has varied greatly, as well as the material with which it is built and the utility, some of them being merely decorative.
Traditionally, the main objective of the construction of a bridge has been to circumvent a type of geographical feature that would prevent (or hinder) the transit due to finding a watercourse, a valley or a precipice. Thus, the bridge is built to connect the most extreme points on both sides and the transfer of different types of means of transport is then allowed to continue. While some bridges are built for the passage of cars and trucks, others are exclusive for trains and railways and others also allow humans to travel on foot. Finally, the famous aqueducts of the Roman period are bridges designed and executed simply for the transfer of water.
The bridges can vary significantly around the material that is used to make them (being some made of wood, others of stone and many other modern of metals such as iron and steel). They can also vary greatly in the type of construction: while some are bridges that are firmly established on the terrain to be circumvented, others are bridges suspended in the air, perhaps more insecure but just as passable.
As has been said, many bridges have been built for ceremonial or symbolic purposes. Although these require the same engineering and construction effort, they are not usually as busy as those that are designed for the transfer of means of transport.
Bridge design, planning and construction work is of great importance as the effectiveness and strength of a bridge must always be ensured. This is related to the weight that a bridge can support as well as the wear and tear that it suffers over time, all issues that undoubtedly must be taken into account when executing the design of a bridge.
