History of Bridges

The technology we use in bridges today was first developed by the great engineers of the Roman Empire. The Romans were not the first to build bridges, but they were the first to build them with strength and withstand nature's conditions. This is the reason we recognize them as the innovators of bridge builders of our past.

During the first to second century AD aqueducts¹ had a great influence on bridges due to our development of the arch structure such as the Corbel and Key Stone Arches². Likewise the Alcantara Bridge that still stands over the Tagus River in Spain, which was built in 105 AD, was another benchmark that the Romans left behind. The bridge had two central arch spans of 110 feet wide that was 210 feet above the Tagus River. To stabilize each arch during construction, temporary timber supports were placed underneath each arch and removed when construction was complete. This technique is still used not only in arch bridge construction but arches we see on buildings and houses. One of the most impressive things about the construction of this bridge was the eight-ton wedge-shape blocks made of uncemented granite. It is incomprehensible that these blocks where only lifted in place using pulleys and homegrown manpower.

Building these bridges and aqueducts were only possible due to the establishment and perfection of cement, concrete³ and the invention of the cofferdam. A cofferdam is a watertight cover that the foundation of the bridge can be constructed in the bed of the river. On the other hand the major type of cement the Romans used was Pozzolana, which was made of water, lime, sand, and volcanic rock.

How the Romans Introduced Concrete⁴

After the time of the Romans, the Chinese started constructing bridges around the year 100 A.D. It has been said that the Chinese borrowed concepts that were already well known in western civilization. Zhang Quian is the Chinese traveler that explored the west to Balkh in 100 B.C., but it was not until the Sui dynasty in 600 A.D. that bridge building peaked.

During this time the most well known bridges in China were far in advance to the western world. This was due to Li Chun who designed the major bridge and founded a bridge design school that was operational for centuries. His most famous bridge to this day is the Zhaozhou Bridge during the Sui Dynasty, completed in 590 A.D. This bridge spans 37 meters over the Jiaohe River and is the world's oldest open-spandrel stone segmental arch bridge. Still today they do not know what principle the Zhaozhou Bridge was built upon.

In the Zhaozhou Bridge⁵ Li Chun used limestone slabs to create twenty-eight thin curved dovetail joints along the central arch of the bridge. This feature gave the arch power to rebalance its weight on the bridge's supports to prevent a virtual collapse, which could occur if a segment of the arch breaks. Also, the two miniatures arches on each side of the bridge were both atheistically pleasing figures and reduced the weight of the bridge. These small arches enabled the bridge to endure the minimal amount of forces during times of flood.