megastructure

thumb|300px|The Great Wall of China, at long, is an ancient era megaproject. This picture was taken near Beijing in February 2005.

A megastructure (or macrostructure) is a very large artificial object, although the limits of precisely how large vary considerably. Some apply the term to any especially large or tall building. Some sources define a megastructure as an enormous self-supporting artificial construct. The products of megascale engineering or astroengineering are megastructures.