Sestertius

The sestertius, or sesterce, was an ancient Roman coin. During the Roman Republic it was a small silver, and rare, coin issued only very occasionally. During the Roman Empire it was a large brass coin. The name sestertius means "2 1/2", the coin's original value in asses, and is a combination of semis "half" and tertius "third", that is, "the third half" (0 1/2 being the first half and 1 1/2 the second half) or "half the third" (two units plus half the third unit, or halfway between the second unit and the third).