Noun – Ornament
1 (count) : a small, fancy object that is put on something else to make it more attractive
She wore a hair ornament.
(US) the hood ornament on a car (=a small metal figure on the front edge of a car’s hood)
Christmas ornaments (=small balls, figures, etc., that are hung on a Christmas tree for decoration)
2 (noncount) formal : a way to make something look more attractive and less plain
A satin bow was used for ornament. (=decoration)
The columns are there purely as ornament—they have no structural function.