Sestertius

The sestertius (pl.: sestertii) or sesterce (pl.: sesterces) 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.

English-language sources routinely use the Latin form sestertius, plural sestertii. Older literature frequently uses sesterce, plural sesterces, since terce is the English equivalent of tertius. A common shorthand for values in sestertii is IIS (Unicode 𐆘). In this sign the Roman numeral II is followed by S for semis, and the whole is written with a horizontal strike. Where this symbol is impractical, HS is often used instead, with the crossbar of H standing for the strike across II.

The sestertius was introduced c. 211 BC as a small silver coin valued at one quarter of a denarius, and therefore one hundredth of an aureus. A silver denarius was set at about 4.5 grams, valued at ten asses, with the silver sestertius valued at two and a half asses at about 1.125 grams. In practice, pieces can be underweight.

When the denarius was retariffed to sixteen asses, a change that followed the gradual reduction in the size of bronze denominations, the sestertius was revalued to four asses while remaining one quarter of a denarius. Republican silver sestertii were produced only sporadically through 44 BC.

In or about 23 BC, during the coinage reform of Augustus, the sestertius was reintroduced as a large brass denomination. The as, now copper, was set at one quarter of a sestertius. Augustus fixed the sestertius at one hundredth of the gold aureus. The sestertius remained the largest regularly issued brass denomination until the late third century AD. Production centered on the mint of Rome. From AD 64, during the reign of Nero and again under Vespasian, the mint of Lyon (Lugdunum) supplemented production of aes coinage.

The brass sestertius typically weighs about 25–28 grams, measures about 32–34 mm in diameter, and is about 4 mm thick. Romans distinguished bronze from brass, calling brass orichalcum, also spelled aurichalcum, a term that alludes to its gold-like color when newly struck.

In the Antonine period the aes coinage shows distinct thematic programs for each denomination while minting evolved. Hadrian used the large orichalcum sestertius for a sustained "travel series" at Rome about AD 130 to AD 133, pairing obverses with reverses that personified provinces such as Britannia or depicted the emperor addressing soldiers during imperial arrivals. Under Antoninus Pius the orichalcum dupondius, identified by a radiate head, announced civic and provisioning programs through reverses for Salus feeding a serpent, Aequitas holding scales, Fides clasping hands, and Africa carrying grain, usually with S C in the fields. Under Marcus Aurelius the copper as stayed the base unit with a laureate portrait of the emperor and reverses that marked the Marcomannic War by showing Germania standing over bound captives.