base
The lowermost portion of a wall, column, pier, or other structure, usually distinctively treated and considered as an architectural unit. Photo from Pisa, Italy, 2018. 2. The level at which earthquake motions are assumed to be imparted to a structure. 3. The line or surface forming the part of a geometric figure that is most nearly horizontal or on which it is supposed to stand, from which an altitude can be constructed. (Ching, 1995)