, dupondius of
Antoninus Pius, and as of
Marcus Aurelius The sestertius was introduced 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. AD 117–138 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. 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. Hostilian had at least seven variations of sestertii minted during his rein. Sestertii continued to be struck until late in the third century. Metal quality and striking declined, although portraiture often remained skillful. Later issues often reused metal from older sestertii. Repeated melting reduced zinc content because zinc boils at about 907 °C while copper melts at about 1085 °C. Mint workers then replaced losses with bronze or other copper alloys, which made later sestertii darker and their preparation cruder. Inflation driven by the debasement of the silver coinage reduced the purchasing power of the sestertius and of smaller denominations such as the dupondius and the
as. In the first century AD daily small change was dominated by the dupondius and the
as. By the second century the sestertius had become the dominant small change in circulation. In the third century the silver content of the coinage fell sharply. The
Antoninianus became the main small coin by the 260s and 270s and it was mostly bronze by that date. Although the antoninianus was theoretically worth eight sestertii, the average sestertius often contained more valuable metal. Some of the last sestertii were struck by
Aurelian (AD 270–275). During the last phase, when sestertii were reduced in size and quality, the
double sestertius was introduced, first by
Trajan Decius (AD 249–251) and later in large quantity by the Gallic emperor
Postumus (AD 259–268). Postumus often overstruck worn earlier sestertii, placing his image and legends over the older fabric. The double sestertius can be recognized by the
radiate crown on the imperial portrait, the same device used to distinguish the dupondius from the
as and the antoninianus from the denarius. Eventually many sestertii were withdrawn by the state or by counterfeiters to melt for the debased antoninianus, which amplified inflation. The coinage reforms of the fourth century did not include the sestertius. ==Unit of account==