Byzantium in Late Antiquity, continuing Roman Imperial systems of coinage, issued three gold coin types and four or five copper types. Beginning in 615, there was also one silver coin type.
The standard was the gold solidus, weighing 1/72 of a Roman pound, or 24 carats (roughly 4.55 grams). At Beth Shean, ten gold solidi, dating from the reigns of Maurice Tiberius through the co-rulership of Heraclius and Heraclius Constantine, were found as a hoard in the Our Lady Monastery. Smaller in value were the gold semissis and tremissis.
The copper follis, worth 40 nummi (the coin of least monetary value), is identifiable by the letter “M” (indicating 40 in Greek). Initially, beginning in the reign of Anastasius I in 498, there were two additional copper coins, the half-follis (worth 20 nummi, marked with a “K”) and a decanummium (worth 10 nummi, marked with an “I”). In 512, a 5-nummi coin (marked with “E”) was introduced, along with the doubling of the weight of the three existing coins. Many of the coins found at the street level in the commercial district and in the Northern Cemetery are folli, including the follis of Tiberius II Constantine found in Room H of the Our Lady Monastery.
Anastasius I in 498 originated a coinage reform to the empire, during which there were four active mints: Constantinople, Thessaloniki, Nicomedia, and Antioch.
After the reconquests of Justinian I in the sixth century, more mints opened in the eastern and western parts of the empire. In the eastern Mediterranean, the primary mints remained Constantinople, Thessaloniki, Nicomedia, and Antioch, in addition to Cyzicus and Alexandria. The chief mints of the western Mediterranean were Carthage and Ravenna.
Inscriptions on coins indicate basic information including the issuing mint, the coin’s value, the ruling emperor, and the year of the emperor's reign.
The names of mints are often abbreviated. Gold solidi were struck with CONOB, CON, and COB, which stood for Constantinopolis together with obryzum (refined gold). Nicomedia is often abbreviated to NIKO, NIK or NIC; Alexandria reads as ΑΛΕΞ or ΑΛΞΟΒ.
The value of copper coins is indicated on the obverse. "M" indicates a follis; "K" a half-folis; "I" a decanummium; and "E" a 5-nummi coin. Also indicated on the obverse are ANNO ("year"), which runs down the left, while a Roman numeral indicates the regnal year of the emperor on the right.
Sometimes, mints were divided into different workshops, called an officina (pl. officinae), and indicated on coins by Greek numerals.
Adapted from Philip Grierson, Byzantine Coinage (Washington, DC: Dumbarton Oaks, 1999).