Concrete

Concrete played a major part in Roman architecture. This versatile building material allowed them to create massive structures, and the fact that it was so easy to use allowed builders to experiment with different shapes and styles. Other civilizations had used concrete before, but always in crude form. The Romans developed a form of concrete that would set under water. The longer it was submerged, the harder it became. Romans used concrete in vaults and tunnels. Even the dome on the Pantheon is constructed of concrete. They also made use of bricks made out of concrete, which became a very popular building material around 200 A.D.

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