A plinth is the base or platform upon which a column, pedestal, statue, monument or structure rests. Gottfried Semper's The Four Elements of Architecture (1851) posited that the plinth, the hearth, the roof, and the wall make up all of architectural theory. The plinth usually rests directly on the ground, or "stylobate". According to Semper, the plinth exists to negotiate between a structure and the ground. Semper's theory has been very influential in the subsequent development of architecture. In its most basic form, a plinth is a plain, rectangular block of stone (curved plinths are relatively rare).