[ProtectOurFreedom]

But small circles? Maybe they invented a compass-plane?

[GingisK]

Of course the Romans had drills and fly cutters. They made engineering marvels.

Once a centrally located drill has embedded into the work, a fly cutter or would be easy to control. Even with a bow saw. The Romans had sophisticated drilling machines.

[GingisK]

Cutting perfect concentric deep-groove circles by hand?

They were smart enough to use a fly wheel on the drill. I'd expect them to be smart enough to make a fly cutter or trepan-like rosette cutter.