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Julian solidus, ca. 361.
Avitus tremissis, one-third of a solidus, ca. 456.

The solidus (the Latin word for solid) was originally a gold coin issued by the Romans, and a weight measure for gold more generally, corresponding to 4.5 grams.


Roman and Byzantine coinage

The solidus was first introduced by Diocletian around 301 AD, struck at 60 to the Roman pound of pure gold (c. 5.3g) and with an initial value equal to 1000 denarii.[1] However, Diocletian's solidus was only struck in small quantities, and thus had only minimal economic impact.

The solidus was re-introduced by Constantine I in 312 AD, permanently replacing the aureus as the imperial gold coin of the Roman Empire. The solidus was struck at a rate of 72 from a Roman pound of pure gold, each coin weighing twenty-four Roman/Greek carats[2], or about 4.5 grams of gold per coin. By this time, the solidus was worth 275,000 increasingly debased denarii.

The solidus maintained essentially unaltered in weight and purity until the 10th century, though in the Greek-speaking world during the Roman period and then in the Byzantine economy it was known as the nomisma (plural nomismata).[2] Whenever the coin was taken in by the treasury, it was melted down and reissued. This maintained the evenness of the weight of the circulating solidi, since the coin did not tend to be in circulation for long enough to become worn.[2]

Minting of the gold coin - unlike the base-metal coins of the time - had no permanently established minting facility. Due to the requirement that taxes were paid in gold, solidus minting operations tended to follow the emperor and his court. For example, solidi were minted in Milan in 353, and in Ravenna after 402. Each of these locations were imperial residences at those times.[2]

Although merchants were forbidden to use solidi outside the Byzantine empire, there was sufficient trade in these coins outside the empire that they became a desirable circulating currency in Arabic countries. Since the solidi circulating outside the empire were not used to pay the taxes to the emperor they did not get re-minted, and the soft pure gold coins quickly became worn.[2]

Through the end of the 7th century, Arabic copies of solidi - dinars minted by the caliph Abd al-Malik who had access to supplies of gold from the upper Nile - began to circulate in areas outside the Byzantine empire. These corresponded in weight to only 20 carats, but matched with the weight of the worn solidi that were circulating in those areas at the time. The two coins circulated together in these areas for a time.[2]

Except in special cases, the solidus was not marked with any face value throughout its seven-century manufacture and circulation[citation needed]. Solidi were wider and thinner than the Aureus[citation needed], with the exception of some lower quality issues from the Byzantine Empire[citation needed]. Fractions of the solidus known as semissis (half-solidi) and tremissis (one-third solidi) were also produced[citation needed].

The word soldier is ultimately derived from solidus, referring to the solidi with which soldiers were paid[3].

Impact on world currencies

In medieval Europe, when the only coin in circulation was the silver penny (denarius), the 'solidus' was used as a unit of account equal to 12 denarii. Variations on the word solidus in the local language gave rise to a number of currency units:



In French language, over the centuries solidus evolved to soldus, then solt, then sol and finally sou. The monetary unit disappeared with decimalisation and introduction of the Franc during the French revolution (1st republic) in 1795, but 5 centimes, the twentieth part of the Franc, inherited the name as a nickname.

To this day, in French around the world, solde means the balance of an account or invoice. Sou is also used as slang for a small coin of little value, as in sans le sou. "I'm broke", "without money".

In Québec sou is also by far the most commonly employed term for the Canadian cent (standard French, cent, rarely used in Québec). Interestingly, quarter dollars in Québec are often called trente sous (thirty cents) because after the English conquest of Québec in 1759, 25 English pennies were the equivalent of 30 French sous and French money continued to circulate there for many years.

Sou of copper, coined 1767 for Louis XV of France


The name of the medieval Italian soldo (plural soldi) was derived from solidus. This word is still in common use today in Italy in its plural soldi with the same meaning as the English equivalent money.

Spain and Peru

As with soldier in English, the Spanish equivalent is soldado. The name of the medieval Spanish sueldo (which also means salary) was derived from solidus, which is also used in the Philippines as Suweldo.

Some have suggested that the Peruvian unit of currency, the sol is derived from solidus, but the standard unit of Peruvian currency was the real up until 1863. Throughout the Spanish world the dollar equivalent was 8 reales ("pieces of eight"), which circulated legally in the United States until 1857. We hear echoes of that time in the expression "two bits" for a quarter dollar, and the real was last used for accounting in the US stock market, which traded in 1/8 dollars until 2001.

The Peruvian sol was introduced at a rate of 5.25 per British Pound, or just under four shillings (the legacy soldus). The term soles de oro was introduced in 1933, three years after Peru had actually abandoned the gold standard. In 1985 the Peruvian sol was replaced at 1000 to 1 by the inti, representing the sun god of the Incas. By 1991 it had to be replaced with a new sol at a million to 1, after which it remained reasonably stable.

United Kingdom

Until decimalisation in the United Kingdom in 1971, the abbreviation s., from solidus, was used to represent shillings, just as d. and £, from denarius and Libra, were respectively used to represent pence and pounds, leading to the abbreviation "£sd".

See also


  • Porteous, John (1969). "The Imperial Foundations". Coins in history : a survey of coinage from the reform of Diocletian to the Latin Monetary Union.. Weidenfeld and Nicolson. pp. 14–33. ISBN 0297178547. 

External links


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