By rotating a circular arc along a vertical axis you can create a circular dome.

The example is of course the Pantheon in Rome. Marcus Agrippinus arised in 27 b.c. a classical rectangular temple and put his signature above the entrance.[br]In 120 emperor Hadrianus rebuilt the tempel and added a round temple to it, covered with a spherial dome.

Only by an aereal view or on drawings you get a good view of the dome.

The cross cut of the Pantheon matches a circle with a perimeter of 43,3 m.[br]Likewise a circular arc, the spherical dome generates enourmous horizontal forces.[br][list][*]The builders tried to reduce the weight of the dome as much as possible. The dome becomes thinner to the top, pumice is used in the concrete and the ceiling is realised with cassettes.[br][/*][*]To support the horizontal forces, the walls of the Pantheon are 6 m thick.[/*][/list]