Instructions
Look first for gold coins. With the exception of the milaresion, first struck under Leo III (717 to 741) and bearing a cross on the front and Greek lettering on the back, the Byzantine Empire made little use of silver. Its most important coin was the gold solidus or nomisma, the preferred currency throughout the Mediterranean during this long stretch of time. There were also half- and third-solidus coins -- called the semissis and tremissis -- although these were discontinued in the late 9th century.
Check next for Christian iconography. A cross was often depicted on the tails of earlier coins, while by the time of Michael III (842 to 867), the heads of the coins usually showed a portrait of Christ or the Virgin Mary. Because Roman currency never employed Christian imagery, this is a good way of telling Roman and Byzantine coins apart.
Look for a portrait of the emperor or empress on either the front or the back of the coin. On the vast majority of currency before and since, portrait busts are usually in profile, or at the very most, offer a three-quarters view of the subject. From the reign of Justinian I (527 to 565), Byzantine coins adopted a style of portraiture where the subject is face-on to the viewer.