Rome itself was opulent during this period. The city of Rome boasted eleven aqueducts, enormous structures that brought fresh water into the city from miles away. The houses of the rich had indoor plumbing with drains that led to public sewers. There were enormous libraries and temples, along with numerous public sites for recreation, including public baths, race tracks, and the famous Colosseum, used primarily for displays of lethal gladiatorial combat.
The empire as a whole enjoyed levels of commercial and agricultural productivity not seen again until the seventeenth century CE. Specialized craftsmen made high-quality goods to be sold on an empire-wide market, with better-off citizens enjoying access to quality tools, dishware, linens, and so on, much of which had been manufactured hundreds of miles away. While the long-term economic pattern was that the wealthier parts of society tended to become even richer at the expense of the common people, there was still a substantial “middle class” that enjoyed a relatively high standard of living.
We should note that, while the Romans are not famous as scientists, they are famous as architects and engineers. The Romans used concrete extensively in building projects. They mastered the art of building arches and domes to hold up ceilings without interior supports. Using only gravity, they could transport water dozens of miles, not just in Rome but in other major cities across the Empire. Roman roads were so well built that some survive to the present, now used by cars rather than the horse-drawn carts they were originally built for.
Each city built by the Romans in their conquered territory was laid out according to careful plans, with streets built in grids and centered on a public forum with public buildings. One of the reasons that the Romans were so effective in assimilating conquered peoples into Roman society was that they built a great deal of infrastructure; being conquered by Rome seemed less like a burden when an aqueduct, public bath, and street system appeared within a generation of the Roman conquest (the relative cultural and religious tolerance of Roman culture was also key). All of these cities were linked by the 40,000 miles of roads that stretched across the empire. The primary purpose of these administrative capitals was extracting taxes and other wealth from the local areas and funneling them back to Rome, but they also served as genuine cultural centers. Likewise, even though the roads were often built with troop movement in mind, people everywhere could take advantage of them for trade.