## About Bridges

The bridge has always been a link that has simplified community living and shortened travel times from one location to another. Bridges have always been a source of fascination for the human being.

Nature built the first bridges as results of erosion from river, sea or ice. The first man-made bridges primitive, built of stone, timber, ropes or combinations of these materials. Probably the first human-crafted bridges were built of timber, which was normally easy to acquire and work with. The earliest historical reference to man-made bridges is one situated over the Nile in year 2650 B.C.E.

Although human beings have used stone since the Stone Age, it wasn't until eight century B.C.E. when human engineers learned to use the arch that stone became the most important bridge material up to the 19th century. The arch remains crucial for the construction of many bridge types, including cantilever, steel truss and suspension bridges.

The first iron bridges were made of chains in China before 600 C.E. The arch bridges made of cast iron appeared in Europe in the 18th century. At the beginning of the 19th century wrought iron bridges came into use, followed by steel bridges. Those materials made to construction of stronger bridges possible, allowing for the spanning of greater distances over rivers and other barriers. This new technology was important to the expanstion of the railroad.

Cement is a very old substance used in bridge construction, dating back to the ancient Roman Empire. The Romans build many strone bridges, using cement as the mortar to bind the stone together. The cement that is in use today had its beginning in 1824. The Alvord Lake Bridge in San Francisco's Golden Gate Park was the world's first reinforced concrete bridge, built in 1889. Since that time, concrete has been in common use in the construction of bridges and overpasses all over the world.

Bridge technology has had a very long tradition in human civilization. The stories of various bridges demosntrate advances in that ancient engineering fete. And those advances continue today as human communities seek to span gulf and gaps to draw families, businesses and governments closer together.

Here are a few bridges that represent the development of these engineering marvels across time.

Nature's Bridges | Ancient/Medieval Bridges | Modern Bridges
--- | --- | ---
Natural Bridge Located in the southern Shenandoah Valley of Virginia. Rainbow Bridge Located in Rainbow Bridge National Monument in southeastern Utah. Sipapu Bridge One of several formations in Utah's Natural Bridges National Monument. | Lugou Qiao An early segmented stone arch bridge located outside of Beijing. Ponte di Rialto Spans Venice's Grand Canal, dating back to the 12th century. Pons Cestius Crosses waters of Tiber River in Rome. | Akashi-Kaikyo Ohashi Japan's Akashi-Kaikyo Bridge is the world's longest suspension bridge. Deception Bridge This bridge crosses Washington's Deception Pass. Lake Pontchartrain Causeway Crosses 24 miles of water north of New Orleans.