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A bridge is a structure used to cross area that
might be hard to get through. Without bridges,
people would have to walk or drive around obstacles like mountains or valleys. Without bridges, people would have would have to use boats to get across water. Bridges make it easier to get from one place to another. There are more than half a million bridges in the United States! The three main types of bridges are beam,arch,and suspension.
Bridges have been around since ancient times.
Bridges have been made from many different things
even rocks,logs,and animal hides.
The first bridges were made by nature. Logs fell across
a stream and people were to cross from one side to the
other. This was the first beam bridge. Flat rocks were also used to cross ditches. Running water, which wore away rock and formed an arch, created the first stone bridge. People used hanging vines as a swing bridge to cross valleys.
Ancient Romans were famous bridge builders. They
built many arched bridges to cross roads and carry
water; these are called aqueducts. Romans needed roads and bridges to connect their huge empire. In England, the London Bridge was built toward the end of the twelfth century. Houses and stores were built on top of it. An old song about this famous bridge is still sung today by children. Covered bridges were very popular in early America and some are still standing. Until about 200 years ago, most bridges were made out of wood or stone. Today, scientists have discovered new materials like steel and concrete that can be used to build longer and stronger bridges.
Although the beam,arch,and swing bridge are very
old types of bridges, they are still in use and probably
the most popular types of bridges being built. Today, we call the beam bridge a girder bridge,the arch bridge is still called the arch bridge, and the idea for a suspension bridge came from the swing bridge. |
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