I think we tend to underestimate what ancient technology could produce because we forget that in ancient times they often operated on longer timescales than we do.
With our technology for example we could make all the parts for the Antikythera mechanism in a short time. The ancient Greeks definitely had no technology that would have allowed them to do that, so we see the existence of the Antikythera mechanism as a great mystery.
But I don't see any reason to believe that the Greeks built it in a short time. It could easily be the lifework of the builder, or even the lifework of successive generations of a family of builders.
If you need to make a very precise gear in a day you need our technology. If you need to make a very precise gear in 50 years you just need someone with an abrasive that is harder than the material you are making the gear from.
With our technology for example we could make all the parts for the Antikythera mechanism in a short time. The ancient Greeks definitely had no technology that would have allowed them to do that, so we see the existence of the Antikythera mechanism as a great mystery.
But I don't see any reason to believe that the Greeks built it in a short time. It could easily be the lifework of the builder, or even the lifework of successive generations of a family of builders.
If you need to make a very precise gear in a day you need our technology. If you need to make a very precise gear in 50 years you just need someone with an abrasive that is harder than the material you are making the gear from.