Mass production of bronze crossbow trigger mechanism, Qin Dynasty (221-206 BCE). This shows high level mechanical engineering, metallurgy, and mass production at the same time.
The Roman Empire vs Chinese civilization debate boils down to the crossbow.
First, there is zero evidence that the Romans mass produced the crossbow. The Ancient Greeks may or may not have. But there is no physical archaeological evidence of any Roman crossbow trigger in any museum anywhere in the world.
Other than the gastraphetes, the only other evidence of crossbows in ancient Europe are two stone relief carvings from a Roman grave in Gaul and some vague references by Vegetius. Pictish imagery dated between the 6th and 9th centuries AD do show what appear to be crossbows, but only for hunting, and not military usage. It's not clear how widespread crossbows were in Europe prior to the medieval period or if they were even used for warfare. The small body of evidence and the context they provide point to the fact that the ancient European crossbow was primarily a hunting tool or minor siege weapon. An assortment of other ancient European bolt throwers exist such as the ballista, but these were torsion engines and are not considered crossbows. Crossbows are not mentioned in European sources again until 947 as a French weapon during the siege of Senlis. From the 11th century onward, crossbows and crossbowmen occupied a position of high status in European militaries,
https://en.wikipedia.org/wiki/History_of_crossbows
The ballista is NOT a crossbow. It is a torsion device relying on two large torsion springs to propel the bolt forward. Those torsion springs are large, heavy, expensive, maintenance intensive, and difficult to scale down into a handheld weapon.
Furthermore, the Romans could not even build complex siege machines like the ballista until after the absorption of the Greek city-states into the Roman Republic in 146 BCE (Battle of Corinth). The Romans COPIED this technology from the Greeks.
Enough about Rome. Now back to China.
In China, crossbows were being employed in large numbers on the battlefield by the middle of the fourth century BC. Some two centuries later, the crossbow had become nothing less than the standard weapon of the Han armies. The Han Dynasty produced the crossbow in the hundreds of thousands.
The Qin Dynasty mass produced the crossbow. China has mountains of archeological evidence to support this fact.
The Han Dynasty continued this mass production.
How powerful was the Chinese crossbow? It could propel an armor-piercing bolt half a mile (800 meters). You would aim upward at a 45 degree angle to achieve this range.
Chinese crossbows were handheld and man-portable. Not a giant siege weapon like the ballista or scorpion.
The Qin had light crossbowman.
The Qin had armored crossbowman.
The Qin had mounted crossbowman.
The Roman Empire is completely outclassed.
Back to 21st century China...