• A large, literate population of educated professionals and engineers not directly associated with the clergy.
• Widespread use of sanitation through aqueducts and sewage systems promoting otherwise impossible heavy urbanization in multiple regions.
• Resource extraction on a scale unrivaled for more than a millennium.
• A dramatic increase in metalworking and smelting so pervasive that it left a spike in the geological record dwarfing measurements from the preceding or following centuries.
• The ability to sustain cities of millions through the use of enormous cargo ships able to transport nearly a hundred tons of grain at a time.
• Extensive use of masonry and concrete.
• Heavy investment in public infrastructure.
• A functional, uniform, widespread system of coinage.
• Burial goods of higher quality and volume than either the prior or following period.
• A large trained and well funded standing army of more than half a million soldiers.
• Construction and maintenance of a widespread network of paved roads stretching thousands of kilometers
• Sustained trade and communication with China and India occurring at a distance and volume not seen again until the 14th and 15th centuries.

ie things that either weren't present or greatly diminished in the years following the collapse of the Roman Empire.