Solidus (coin) - Roman and Byzantine Coinage

Roman and Byzantine Coinage

The solidus was first introduced by Diocletian around 301 AD, struck at 60 to the Roman pound of pure gold (and thus weighing about 5.5 g each) and with an initial value equal to 1,000 denarii. However, Diocletian's solidus was struck only in small quantities, and thus had only minimal economic effect.

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

The solidus was 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). 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 long enough to become worn.

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 be 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. These locations were imperial residences at the respective times.

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 Arabian countries. Since the solidi circulating outside the empire were not used to pay taxes to the emperor they did not get reminted, and the soft pure-gold coins quickly became worn.

Through the end of the 7th century, Arabic copies of solidi—dinars minted by the caliph Abd al-Malik ibn Marwan, 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 (4.0 g), but matched the weight of the worn solidi that were circulating in those areas. The two coins circulated together in these areas for a time.

Except in special cases, the solidus was not marked with any face value throughout its seven-century manufacture and circulation. Solidi were wider and thinner than the Aureus, with the exception of some lower-quality issues from the Byzantine Empire. 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.