#pendentives

Byzantine architects learn to construct round domes over square rooms. They used four pendentives, triangles cut from a circle to provide a round base on which the dome rests. The pendentives shift the weight of the dome to the four supports below.

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For many years the dome of the Pantheon, in Rome, Italy, baffled modern engineers. They did not know how the ancient Romans managed to build such a large dome. Then they discovered that the dome was made of concrete that becomes lighter as it gets higher because each level is mixed with lighter stones such as volcanic pumice.

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