Smart people. Who knew?
A while back at a Pompeii show, I was able to see a 2000 year old bronze or brass water valve. It was the same cone type you would see on a wine barrel. It was amazing to think the Romans had that level of machining ability.
Eli Witney built firearms starting in 1798 with interchangeable parts.It's amazing that they could make stuff like that at all. I think they were probably doing it all by hand and there were no interchangeable parts without even more handwork to make another or, if they got lucky, found a part that was too big and could "file" it down to fit.
The early guns, and cars to some degree, didn't have interchangeable parts even though all the parts looked pretty much the same. I wish I remembered when they both got better but in the early 1900s Cadillac had four cars completely disassembled in the same room with no parts marked and succeeded at getting all four back together and running by just grabbing whatever part they needed next.
Unfortunately, a lot of technology gets lost due to the ups and downs of the human condition. Sometimes all it takes is a volcanic eruption or widespread disease.Lots of OOPARTS (out of place artifacts) out there. I've seen citric acid batteries, studied the Piri Rei's map, an Islamic map that cites source maps that are very ancient when the entire world was mapped very accurately. How they mapped it is still unknown to my knowledge since a lot of knowledge is required to do it. Much more. Seems ancient history is not what the modern West has reconstructed it to be. If we only had the library at Alexandria we would probably be able to reconstruct it much, much more accurately and make sense of the evidence of an ancient high technology.