How the Romans became the most powerful empire in the world prior to the Dark ages?

The Romans were able to build a vast and powerful empire mainly through their military, which was virtually unrivaled at the time. Continued expansion of the empire (especially across the eastern regions of Egypt, Greece, Judea, and Anatolia) brought unprecedented wealth to the empire. This wealth contributed to even more expansion and development across Gaul (France), Spain, and even up to modern-day Great Britain.

The Romans built upon their success which basically helped them dominate most of Europe for a millennium.