A denarius (plural: denarii) was the main silver coin used in ancient Rome for over 400 years. If you traveled back in time to Rome around 200 BC, a denarius would be like having a twenty-dollar bill in your pocket: valuable enough to matter, but common enough to use for everyday purchases.

A skilled Roman worker might earn one denarius for a full day's labor. With it, you could buy about ten pounds of wheat, enough to feed a family for several days. The coin itself was roughly the size of a modern dime but made of solid silver, with the emperor's face stamped on one side and various symbols on the other.

The denarius appears in the Bible, where it's sometimes translated as “penny” in older English versions. When Jesus asked whose face was on the coin, he was holding a denarius. When the workers in his parable agreed to work for a denarius a day, that was considered fair pay.