sestertius

The sestertius (: sestertii) or sesterce (: sesterces, rarely sestercii) was an ancient Roman coin. During the Roman Republic it was a small silver coin issued only on rare occasions. During the Roman Empire it was a large brass coin.

The name sestertius means "two and one half". It refers to the nominal value of two and a half asses, a value useful in commerce because it was one quarter of a denarius, a coin worth ten asses. The etymology is ancient. Latin writers derive sestertius from semis "half" and tertius "third", where "third" points to the third as, since two asses and half of a third equal two and a half.