How did the roman empire prosper during the reign of the Five good emperors

Depends on Emperor, but mainly was the army. The army conquered many lands such as the land now called England. They even got as fair to Asia, before being pushed back. As well when conquering those lands, they gained Servus or slaves. That could then go to be a Tiro, or Auxilia. With all of that brought power and wealth. As well a lasting image of how terrifying the empire was.