Sol LeWitt's Four-sided Pyramid

From www.nga.gov:

From the early 1960s to the present, Sol LeWitt has been at the forefront of minimal and conceptual art. LeWitt's "structures" (a term he prefers to sculpture) are generally composed with modular, quasi-architectural forms. For many of his works, LeWitt creates a plan and a set of instructions to be executed by others. Four-Sided Pyramid was constructed on this site by a team of engineers and stone masons in collaboration with the artist. The terraced pyramid, first employed by LeWitt in the 1960s, relates to the setback design that had long been characteristic of New York City skyscrapers. Its geometric structure also alludes to the ziggurats of ancient Mesopotamia.