At the beginning of the fourth century CE, the Roman Empire found itself in a prolonged economic decline. Centuries of warfare and misrule had slowly eroded all aspects of Roman life. Unsurprisingly, this was reflected in the Roman gold coins of the era. The gold aureus, a staple of Roman commerce for the better part of four centuries, had been reduced to an almost unrecognizable state and was in dire need of an overhaul.
To this end, the solidus was introduced circa 310 in the Western part of the empire by Constantine I ‘the Great’ (307-337). The new gold standard of the empire, the solidus was struck at the lighter weight of 72 per pound (about 4.5 grams) on a comparatively broad and thin planchet. This impressive solidus of Constantine I, struck at Antioch in about 324, features a portrait of Constantine I on the obverse and the figure of the emperor on horseback on the reverse.
Solidus of Constantine I “The Great”. All images courtesy Classical Numismatic Group (CNG)
The solidus remained the standard gold coin for the rest of the Roman Empire and filled the same role for most of Byzantine history. Its only period of weakness during the Roman Empire was circa 346 to 368, when its fineness dropped from the usual 99%+ to slightly less than 95%.
When it was restored to its traditional purity in 368, some mint signatures began to include the letters OB, abbreviating obryzum, meaning ‘pure gold’. This solidus of Gratian (367-383) was minted at Sirmium c. 379-380, and displays just such an inscription in the exergue on the reverse, after “SIR” (used to indicate Sirmium as the mint). The coin features a portrait of the emperor on the obverse and an ornate scene of the seated figures of the co-emperors (and half-brothers) Gratian and Valentinian II on the reverse.
Restored solidus of Gratian (minted c. 379-80), featuring the emperor and his brother Valentinian II on reverse
On some occasions the weight of a Roman gold coin was indicated with a supplemental inscription. For example, during the Tetrarchy (c. 284-313) the Greek letters Xi and Omicron occasionally appear in the reverse fields, indicating coins that were struck, respectively, at 60 and 70 to the pound. Some Constantinian solidi bear the Latin inscription LXXII, a clear indication that they were struck at 72 to the pound. This solidus of Constantine I is an example of this practice, as the LXXII on the reverse indicates the weight standard. Minted at Antioch circa 335-336, it features the portrait of Constantine I on the obverse and Victory holding a palm frond and trophy on the reverse.
Solidus of Constantine I (Victory on reverse) with indication of weight
Two less common gold coins of the late empire were the semissis and the 1 ½ scripulum, both introduced by Constantine the Great. The first was (as its name suggests) half of a solidus, and the second was an odd denomination of about 1.7 grams, which is sometimes called a nine-siliqua. Neither of these coins played a significant role in the Roman economy, though the semissis was struck in very large quantities as a Byzantine coin starting in the sixth century.
This semissis of Valentinian III (425-455), struck at Constantinople early in his reign, displays the emperor’s bust on the obverse and Victory inscribing a shield on the reverse.
Gold semissis of Valentinian III
Far more important was the tremissis, a one-third solidus that weighed about 1.5 grams. It was introduced c. 383, but was not widely used until about 430. It became a great success, especially since the denomination was popular with Germanic peoples. This tremissis in the name of the Roman emperor Julius Nepos (474-475) was actually struck by the Visigoths in imitation of a legitimate Roman issue. The style is slightly crude, but still recognizable.
Tremissis featuring Julius Nepos (474-75) struck by Visigoths
By contrast, this imitative tremissis, struck by the Merovingians circa 561-613, is so devolved as to be almost unrecognizable.
Merovingian tremissis, struck c. 561-613
In the name of Justin II (565-578), it features a distorted portrait on the obverse and a highly stylized Victory on the reverse.
In addition to these fractional coins, multiples – considered medallions – were also struck. The smallest was the 1 ¼th solidus, essentially a revived aureus, which today is called a ‘festaureus’ because it is thought to have been a ceremonial coin.
As the Roman Empire gave way to the Byzantine Empire, this system of gold coinage would continue into the ninth century, when dramatic changes would be made once again as the empire attempted to right itself in the face of near-collapse.