What numbers might encourage a Texas cowboy to re-up for another cattle drive? Explain

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.