A solidus (the Latin word for solid) was originally a gold coin issued by the Romans. It was introduced by Constantine I in 309–10, and was used through the Byzantine Empire until the 10th century. The coin replaced the aureus as the main gold coin of the Roman Empire.

The name solidus had previously been used by Diocletian (284–305) for the gold coin that he introduced, which is different from the solidus introduced by Constantine. The coin was struck at a theoretical value of 1/72 of a Roman pound (about 4.5 grams). Solidi were wider and thinner than the aureus, with the exception of some dumpy issues from the Byzantine Empire. The weight and fineness of the solidus remained relatively constant throughout its long production, with few exceptions. Fractions of the solidus known as semissis (half-solidi) and tremissis (one-third solidi) were also produced.

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

Impact on world currencies

Variations on the word solidus gave rise to a number of currency units:

France

In France the sou (until 1715 sol or solt) was the name of a coin. It was first minted in gold, from the 1200s in silver and during the 1700s in copper. The sou tournois was a 12-denier coin, one-twentieth of the livre tournois (Tournois pound), while the sou parisis was a 15-denier coin. After decimalisation in France, the sou became the name for a five-centime coin, one-twentieth of the French franc (Until the late 1960s, the expression "20 sou" was a synonym for 1 Franc).

To this day, sou is used as slang for money, as in j'ai pas de sous. "I'm broke", "I haven't got two bob to rub together". It is also a slang term for the Canadian cent (standard French, cent).

Italy

The name of the medieval Italian soldo (plural soldi) was derived from solidus.

United Kingdom

Until decimalisation in the United Kingdom in 1971, the abbreviation s., from solidus, was used to represent a shilling, worth one-twentieth of a Pound Sterling, just as d. stood for denarii (pennies) and £ stood and still stands for Libra (pound), leading to the abbreviation "£sd". Though the shilling and its abbreviation are no longer used, a slang word for shilling, "bob", is still occasionally used in expressions like "a few bob", i.e. a small amount of money.

See also

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• Roman currency
• Byzantine coinage
• Slash (punctuation) (also called a solidus)

Coins of Ancient Rome | Gold coins

Solidus | Solidum | Solidus | Solidus (monnaie) | Solido (moneta) | ソリドゥス金貨 | Солидус (монета) | Solid | Су (монета) | Solidus