The Roman Pantheon was built in 27 B.C. and rebuilt in 126 A.D. out of concrete and still stands today as the world's largest unreinforced concrete dome. The dome has a height and a diameter of 142 feet. Because of concrete's versatile nature, builders were able to construct an inner honeycomb system which reduced the total weight of the dome and put less stress on the structure. Concrete also allows the dome to have sunken panels on its interior in five rows of twenty-eight.
The Sagrada Familia church in Barcelona, Spain, was designed by Antoni Gaudí and uses concrete to allow for its complex mix of modern and Gothic details. Because of that complexity the building remains under construction after being dedicated in 1882. The church contains plans for 18 spires as well as many elaborately decorated facades, containing different animals and scenes from the Bible. Inside the building a large concrete staircase is planned which will be decorated with demons, idols and false gods.
The Casa Batllo is another building designed by Antoni Gaudi in Barcelona, Spain, which uses concrete design flexibility to obtain a fluidity in its facade. The Casa Batllo was built in 1877 and remodeled in 1904. Among Casa Batllo's most unique features are its irregular oval windows and flowing sculpted concrete work. Casa Batllo's roof, staircase and chimney structure also have curving designs because of the sculpted concrete in its construction.
Frank Lloyd Wright's design of the Guggenheim Museum was the last of his career, but offered an innovative concrete design with a conical shape outside. Inside the building, the viewing gallery is made up of a gentle spiral from the first level to the top floor. The museum displays its art on the walls of the spiral. The exterior of the building was restored starting in 2005 to ensure its structural integrity.