Getting Started with Roman Coins - Monetary Reform of Augustus in 23 BC

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The Imperial Period (27 BC to 476/491/498 AD)
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Monetary Reform of Caracalla in 215 AD

Imperial coinage started with the monetary reform of Augustus in 23 BC which standardised on the following denominations:

MetalDenominationValue (Asses)Value (Denarius)Weight
GoldAureus400257.8g
Quinarius aureus (Half Aureus)20012.53.89g
SilverDenarius1613.79g
Quinarius8½1.73g
OrichalcumSestertius4¼25g
Dupondius21/812.5g
CopperAs11/1610.5g
OrichalcumSemis½1/324.6g
CopperQuadrans¼1/643.6g

The old bronze denominations that survived were now minted either in copper or orichalcum (a brass alloy of 80% copper and 20% zinc), and the Sestertius was reintroduced using orichalcum instead of silver.

Denomination
Aureus

7.86g
20.5mm

Quinarius aureus (Half Aureus)
3.94g
15mm
Denarius

3.35g
19.5mm

Quinarius

1.78g
14.5mm

Sestertius

25.28g
33mm

Dupondius

14.31g
25mm

As

9.17g
24.5mm

Semis

5.74g
20mm

Quadrans

2.77g
17mm

The Dupondis and As were of a similar size, but could be identified at the time by their colour. Orichalcum has a yellow colour, and copper a red colour. This sometimes presents difficulties for collectors as the colour can now be obscured by patina. In 66 AD, Nero changed the portrait on the Dupondius so that the emperor had a radiate crown instead of the classical laurel crown (for women, a crescent under the bust).

Coins from Augustus onwards feature a portrait of the emperor (or a relative) on the obverse. The taboo of having a living person on a coin was comprehensively broken during the Imperatorial era.

The monetary reforms of Augustus lasted for about 200 years. In that time the coins were debased by Nero in 66 AD amongst others, and by 200 AD purity had declined by as much as 50%. It should be noted that some emperors, such as Pertinax, tried to reverse the debasement.

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