Sculpture is one of the oldest art forms and has a rich history that stretches back to some of the earliest civilisations. But as with other art forms, the styles of sculpture have changed and diversified into different types that reflect the prevailing trends of the period. Today there are many forms of sculpture. They can overlap, but there are several distinct categories that most modern and classical sculpture can be divided into.
According to the Metropolitan Museum of Art's Heilbrunn Time line of Art History, Relief sculpture is "sculpture that projects in vary degrees from a two-dimensional background." Relief sculpture is among the oldest forms of sculpted art. The Crafty Art World website breaks down Relief sculpture into three major types, based on how far out from the two dimensional background the sculpture rises. Bas-relief has a very low degree of relief from the base, and is present in the surfaces of famous buildings such as the Parthenon in Greece. Alto-relief sculpture has a high degree of relief; the sculptures emerge from the flat base background, such as the sculptures of ancient pharaohs on their temples in Egypt. Sunken-relief sculptures are actually carved into the base itself and have a negative degree of relief.
Free-standing sculpture, also known as sculpture in-the-round, likely represents the form of sculpture most recognisable to modern people. Free-standing sculpture is any work of sculpture which can be viewed from any angle around the pedestal. This kind of sculpture includes some of the most famous works of sculpture throughout time: the statuary works of the Greek, Roman, Medieval and Classical eras, including Michaelangelo's David. Another work of even more ancient free-standing sculpture is Glykon's Hercules, as seen on the University of Southern California at Los Angeles's website on statuary found within the Baths of Caracalla, in Rome. In the modern era, statuary and free-standing sculptures are still being used to glorify the achievements and legacies of important historical figures. One of the most famous statues of George Washington was carved by Horatio Greenough in 1840 and now rests, according to the Smithsonian Press - Legacies website, within the Smithsonian Museum of History and Technology in Washington, D.C.
Kinetic sculpture is free-standing sculpture that moves, either by mechanical power or under the power of wind or water. Fountains are a form of kinetic sculpture, although in that special case the sculpture is not powered by the water but lives within the shapes and forms of the water as it arcs over and through the air.
Another more modern form of sculpture is known as Assemblage sculpture, which is sculpture pieced together from found or scavenged items that have little or no relationship to one another. Contemporary Art Dialogue's website defines assemblage art as "non-traditional sculpture, made from recombining found objects. Some of these objects are junk from the streets." These pieced-together bits of castoff debris are arranged in an aesthetically pleasing shape to the artist and then presented to its audiences to provoke thought and reaction. Collages are a sort of two-dimensional representation of assemblage sculpture.