Solidus (coin)

The solidus (Latin for "solid"; pl. solidi), nomisma (Greek: νόμισμα, nómisma, lit. "money"), or bezant was originally a relatively pure gold coin issued in the Late Roman Empire. Under Constantine, who introduced it on a wide scale, it had a weight of about 4.5 grams. It was largely replaced in Western Europe by Pepin the Short's currency reform, which introduced the silver-based pound/shilling/penny system, under which the shilling (Latin: solidus) functioned as a unit of account equivalent to 12 pence, eventually developing into the French sou. In Eastern Europe, the nomisma was gradually debased by the Byzantine emperors until it was abolished by Alexius I in 1092, who replaced it with the hyperpyron, which also came to be known as a "bezant". The Byzantine solidus also inspired the originally slightly less pure Arabian dinar.

In late Antiquity and the Middle Ages, the solidus also functioned as a unit of weight equal to 1/72 of a pound.

Roman and Byzantine coinage

The solidus was introduced by Diocletian in AD 301 as a replacement of the aureus, composed of relatively solid gold and minted 60 to the Roman pound. His minting was on a small scale, however, and the coin only entered widespread circulation under Constantine I after AD 312, when it permanently replaced the aureus. Constantine's solidus was struck at a rate of 72 to a Roman pound (of about 328.9 g) of pure gold; each coin weighed 24 Greco-Roman carats, or about 4.5 grams of gold per coin. By this time, the solidus was worth 275,000 increasingly debased denarii.