Hemiobol

Poseidonia — the Greek colonial city on the Tyrrhenian coast of Lucania known to the Romans as Paestum — issued fractions like this hemiobol to facilitate small-scale commerce in a region where trade with indigenous Italic peoples demanded a full range of denominations. At roughly a quarter-obol's worth of silver, these pieces were among the smallest practical units the mint produced, and surviving examples are correspondingly scarce; the attrition rate for coins this light in ancient circulation was brutal.