A Sculpture is the branch of the visual arts that operates in three dimensions
Interesting, I am an artist and do admire sculptures. 
Durable sculptural processes originally used carving which is really hard to  do.
I bet they were difficult considering they didnt have much tools back then like we do today
Sculpture in stone survives far better than works of art in perishable materials and they are the ones that look the best in my opinion
Yes I agree stone lasts thousands of years of kept out of the rain. 
 Sculptures have been central in religious devotion in many cultures and many other things l
Yes some have even been used as idols in many cultures.
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Sculpture in stone survives far better than works of art in perishable materials, and often represents the majority of the surviving works (other than pottery) from ancient cultures, though conversely traditions of sculpture in wood may have vanished almost entirely. However, most ancient sculpture was brightly painted, and this has been lost.
Sculpture has been central in religious devotion in many cultures, and until recent centuries large sculptures, too expensive for private individuals to create, were usually an expression of religion or politics. Those cultures
Sculpture
Sculpture is the branch of the visual arts that operates in three dimensions. It is one of the plastic arts. Durable sculptural processes originally used carving (the removal of material) and modelling (the addition of material, as clay), in stone, metal, ceramics, wood and other materials but, since Modernism, there has been an almost complete freedom of materials and process. A wide variety of materials may be worked by removal such as carving, assembled by welding or modelling, or molded or cast