Any tips on how to make an "indent"?

I’m trying to model part of a cobblestone bridge, like the one in the picture. I can just use a displace modifier for the smaller cobblestone, but I’m wondering if there’s any trick where I can model the indents in the bigger flagstones on the bridge, rather than just raw modeling, which would take a while on my model.

EDIT: Here’s a screenshot of my model so far. I want to have indents on all of the inner edges on the upper circular loop, like in the picture.

If i understand well what you need, here’s an example with a very simple and fast method but that should work nice

Have your model having this kind of topology (looks like your is good for that) at the rounded part

In Face selection mode, select those faces

Press ALT+E and select “Individual Faces”

Then extrude a bit

Still in Face selection mode, change the Pivot to Individual Origin

Press S and scale only a bit

That should work. Thanks for the help!