like this question, but my part is from the pillar body itself, how you create this rounded half circle surrounding perfect in rounded pillar?
You could add a cylinder and inset each face (I to inset, then F6 and change to 'individual'). Then extrude inward and bevel the edges as necessary.
The result looks like this. The geometry may be difficult to work with if you're using a subdivision surface, in which case I would add extra loop cuts on the edges between the insets to connect horizontally.