Interior of a dome structure, hemispherical shape evolved from the arch and forming a roof. A dome can rest directly upon walls, columns, or a system of pendentives used to support the transition of shape from a building base to the round base of the dome. There are many variations on this shape and how it is supported. However, in this case there are six ribs that intersect at the apex of the dome and rotates around its vertical axis. They were prominent in Persian, Roman, and Byzantine architecture. Famous examples of domes that exist today include the Taj Mahal, US Capitol and cathedrals found across Europe.