"A column or pillar in is a vertical structural element that transmits, through compression, the weight of the structure above to other structural elements below." (abstracted from Google Wiki)
Column and pillar are different from size. The big one is called column, small one is called pillar.
Columns have 3 parts. The top part is called column capital (Roman column / Roman pillar has the round capital), the middle part is called column shaft; the bottom part is called column plinth or column base. China Stones Inc. could produce column and pillars in curved column slab or in solid piece as long as 7 meters (275").
Stone column (stone pillar) could be produced with many natural stones such as granite column (granite pillar), marble column (marble pillar), sandstone column (sandstone pillar), limestone column (limestone pillar).