what factors contributed to the rise of both the han dynasty and the roman empire ?

idk much about he han dynasty but roman in particular used slave labor. That was a big factor in contributing to their massive stuctures. also, they had many extraordinary engineers that created amazing aquaducts, bridges, and awesome complex buildings that all increased the efficientcy of their empire more so than any other at the time. They were the only ones that really used concrete, a mixture of cement and volcanic ash, which allowed for more massive, stronger, and lighter buildings. concrete also allowed them to build tings in water like docks and bridges. There are many more subtle things the romans did, but those are the main ones i can think of.

You raise some good points in your question.