Egypt's Pyramids (5000 B.C.) could be seen as a series of conceptual pieces (installations in the dessert?). In his Introduction to Aesthetics, G. F. Hegel compares the pyramids to the beginning of the development of the “Idea.” (For some, “All triangles have three sides” is an a priori proposition). In his 1972 “Art History,” John Baldessari uses a similar photo to imply the same idea.