Roman Units & Currency

The Primary Denominations

Sestertius of Hadrian (Spink 638a, RIC 913; A.D. 122; extremely rare)

‘Hadrian Augustus, three times consul, father of his country.’
Reverse: EXERC BRITANNICVS S C ‘For the army of Britain, by order of the Senate.’
Coin currently in B.M. Department of Coins and Medals (gallery 49, case 14) on loan from the collection of G. Cope.

Standard set by Augustus

The emperor Augustus made a great many reforms during his years in office (27BC-14AD), and in 24BC the Roman monetary system came under his close scrutiny. His standardised coinage was minted in seven denominations using four different metals; gold, silver, brass and copper.Standard set by Augustus

Monetary Relationships (first to third centuries)
aureus denarius sestertius dupondius as semis quadrans
(gold) (silver) (brass) (brass) (copper) (brass) (copper)
1 25 100 200 400 800 1600
  1 4 8 16 32 64
    1 2 4 8 16
      1 2 4 8
        1 2 4
          1 2

These basic denominations were augmented or replaced by various other coinage issues, particularly during the frequent economic crises of the later empire.

The Primary Denominations

Aureus – Gold

aureus (pl. aurei) ‘golden’, from aurum ‘gold’.

The Aureus was the highest denomination coin of the old Republic, and remained so for most of the Roman Imperial period. They were minted in gold of a very high purity, and valued at twenty-five denarii or silver pieces. The weight fixed by Augustus at the beginning of the first century was 7.75 grammes, and this remained fairly constant up until the reign of Septimius Severus (193-211AD) when it weighed around 7.2 grammes, but by the reign of Gallienus (253-268AD) this had been reduced to only 2.45 grammes. Throughout this time the purity of gold used to make the aureus remained fairly constant, with the result that the coin became somewhat reduced in size.

Denarius – Silver

denarius (pl. denarii) ‘containing ten’, from decem ‘ten’; originally worth ten asses.

During the early Republic these silver coins were struck in almost pure metal, but by the time of Claudius the coin had been debased, and contained a significant quantity of copper alloyed with around 3.5 grammes of silver. The weight and fineness of the denarius fluctuated markedly throughout its lifetime, and the intrinsic silver content was constantly being reduced, so that by the middle of the third century, during the reign of Gallienus, the silver content was only 0.08 grammes. The introduction of the antoninianus into the monetary system by Emperor Caracalla quickly forced the denarius out of circulation, and after 244AD denarii were no longer issued with many being over-struck by the state and converted into antoniniani.

Sestertius – Brass

sestertius (pl. sestertii or sesterces) ‘two and a half’; originally worth 2½ asses.

Made from orichalcum,¹ a mixture of copper and tin somewhat like brass. These coins were minted in large quantities during the republic, but their value declined during the empire making their production no-longer economical.

The sesterce was represented in writing by the Latin symbols for 2½, properly IIS. The symbol S representing the fraction was standard Latin shorthand for semis, meaning ‘half’. In latter times IIS became transformed to HS, which is the most commonly recognized modern format.

  1. orichalcum is also the Latin name for Yellow Copper Ore.

As – Copper

as (pl. asses or assis) from aes ‘copper’.

This was the standard monetary unit and Copper coin of ancient Rome. The as and its diminutives, the semis ‘half-piece’ and quadrans ‘quarter-piece’ were produced in vast quantities during the Republic but with galloping inflation they became almost valueless by the second century AD. The word as, Latin for ‘unity’, is thought to stem from the ancient Etruscan language. The as was also an early Roman unit of weight, approximately equal to 1 pound Troy or 373 grammes.

Other Coin Issues and Denominations

  • Aes grave ‘heavy copper’; another name for the dupondius.
  • Antoninianus (antoniniani) This silver coin introduced by Caracalla was worth 2 denarii and was named after his family. The weight and fineness of these coins rapidly declined, and by the reign of Claudius II Gothicus (268-270AD) the weight had been reduced to only 2.75 grammes, containing only 2% silver.
  • Argenteus This silver coin was introduced by Diocletian c.293AD to replace the ailing antoninianus. It contained around 3.4 grammes of silver, and was tariffed at one-hundred denarii.
  • Dupondius A brass coin worth two copper asses. The name stems from Latin duplex ‘twofold, double’.
  • Follis: Issued during the monetary reforms of Diocletian c.295AD, these coins weighed around 10 grammes and contained 3% silver. They were intended as a replacement for the sestertius.
  • Nummus: Another name for a sestertius.
  • Quinarius: These coins were issued on occasion during the early empire, in both gold and silver denominations, equal in weight to half an aureus and half a denarius respectively.
  • Solidus: This gold/silver coin was first issued by Constantine to replace the pure gold aureus. Its name stems from the Latin verb solido ‘to consolidate’; what Constantine hoped to do by debasing his gold coinage.

Roman Linear and Volumetric Measures

Units of Length

  • 1 uncia ‘twelfth part’ = approx. 1 inch
  • 12 unciae ‘inches’ = 1 pes ‘foot’ = 29.59cm
  • 5 pedes = 1 passus ‘pace’ = 1.48m
  • 125 passuus = 1 stadium ‘race-track’
  • 8 stadia = mille passuum ‘one-thousand paces’ = 1 Roman Mile = 1.48km = 1,620yards

Units of Area

  • 100 pedes quadrati ‘square feet’ = 1 scripulum
  • 144 scripula = 1 actus quadratus
  • 2 actus quadrati = 1 iugerum
  • 2 iugera = 1 heredium
  • 100 heredia = 1 centuria

Units of Weight

  • scripulum ‘scruple, a small weight’
  • 4 scripulae = 1 sextula ‘a sixth part’
  • 6 sextulae = 1 uncia ‘a twelfth part’ = approx. 1 ounce
  • 12 unciae ‘ounces’ = 1 libra = 1 Roman pound = approx 11½ oz. or ¾ lb. avoirdupois.

Units of Volume or Capacity

  • 4 cochlearia ‘snailshells’ = 1 cyathus ‘ladle, wine-measure’ = ?
  • 12 cyathi = 1 sextarius ‘one-sixth measure’ = approx. 1 pint
  • (liquid)
    • 6 sextarii = 1 congius¹
    • 8 congii = 1 amphora²
    • 20 amphorae = 1 culleus
  • (dry)
    • 8 sextarii = 1 semodius ‘half-modius’
    • 2 semodii = 1 modius³ = approx. 1 peck

  1. Related to the word congiarium, a largess for soldiers, usually in the form of a measure of corn, oil, wine etc.
  2. An amphora was a large, two-handled earthenware jar of a standard size, used to transport foodstuffs such as olive-oil, cereals and wine.
  3. An interesting example of a modius measure was found outside the fort at Magnis (Carvoran, Northumberland) on Hadrian’s Wall.

A Comparative Chronology of Money – From the University of Exeter

References for Roman Imperial Coinage

  • Coins of England and the United Kingdom – Spink Standard Catalogue of British Coins by Spink (Spink & Son, London, 37th Ed., 2002);
  • The Romans : An Introduction by Anthony Kamm (Routledge, London, 1995);
  • Roman Coinage in Britain by P.J. Casey (Shire Archaeology, 1994);