The primary currency used in the Roman Empire was the denarius. Introduced around 211 BCE, the denarius was a silver coin that became the standard currency for trade and commerce throughout the empire. It facilitated economic activity across vast territories, helping to unify the diverse regions of the empire through a common medium of exchange. The denarius was widely recognized and utilized in military pay, commerce, and the taxation system. As the empire expanded, the coin evolved in terms of material content and design but remained central to the Roman economy for centuries.