[Forward the Light Brigade]

Roman ships got to China. The pagan Romans painted eyes on their ships. The Chinese say that and thought it was cool and started to put eyes on their junks. Romans had a counting board—Chinese copied and improved it as the Abacus. Lots of trade went on at one time. Chinese invented the crossbow—Romans were impressed with it and improved it.

[Hugin]

More likely the crossbow was invented independently in the west and east. The Greeks had the gastraphetes (belly-bow) as far back as the 5th century BC. The Romans probably got it from them.