Hollow COLUMN is that which has a spiral staircase in the inside, for the convenience of ascending to the top; as the Trajan column, the staircase of which consists of a hundred and eighty-five steps, and is illuminated by forty-three little windows, each of which is divided by tambours of white marble. The Monument or fire-column at London has also a staircase, but it does not reach to the top. These kinds of columns are also called columnae, coelideae, or cochlidae.