Cosmas Indicopleustes, a sixth-century a.d. merchant, observed that the eastern Roman Empire owed its prosperity to two causes, Christianity and coinage. The history of these two valued attributes of the eastern empire leads back to one person, Constantine I, who made Christianity the official religion of the Roman Empire and introduced the golden solidus coin, which the Byzantine Empire continued to mint without debasement until the eleventh century.
Constantine rose to power in a portion of the western empire in a.d. 306, and after nearly two decades of piecemeal war with rivals, made himself sole emperor of the Roman Empire in a.d. 323. The Roman Empire had been in the clutches of rampant inflation for half a century. The emperor Diocletian had issued full-weighted gold and silver coins, but the inflation showed no signs of easing up. In a.d.
301 Diocletian issued his famous Edict of Prices, which made raising prices above legal limits a capital offense. The Roman government had continued to debase its silver and copper coinage, but it had never significantly reduced the weight or purity of its gold coins. With inflation still out of control, Constantine put the reform of the currency close to the top of his priorities.
Constantine minted the solidus at a weight equal to one seventy-second of a pound of gold. Each pound equaled 12 ounces, and each ounce equaled 24 scruples. A solidus weighed 4 scruples. The greatest challenge Constantine faced was finding adequate supplies of gold and silver bullion. He required that a certain share of taxes be paid in silver and gold and he enacted new taxes payable in silver and gold. Also rents on imperial lands were collected in gold. He inherited a practice from previous emperors of placing a levy on cities in gold bullion. His most famous action to secure large supplies of gold and silver, enabling him to launch new gold and silver coinage on a large scale, was the seizure of the gold and silver stored in pagan temples. In the words of an anonymous observer writing a generation later:
In the time of Constantine there was lavish expenditure: he assigned gold to mean transactions, instead of bronze, which formerly used to be held of high value. The origin of this avarice is believed to have come from the following cause. When gold and silver and a great quantity of precious stones, which had been stored in ancient times in the temples came into public use, it inflamed the desire of all for giving and possessing. And whereas the expenditure even of bronze … already seemed heavy and excessive, nevertheless owing to a kind of blindness there was a more lavish zeal for expenditure in gold, which is considered more valuable.(Jones, 1964)
During the time of Constantine, the solidus was mainly used to pay large government expenditures, but it steadily grew in popularity as a means of settling private transactions. During the fifth century a.d., both the eastern and western governments discontinued all but the smallest copper coins, and silver coinage also dropped to a trickle. Gold coinage became the principle medium of exchange for public and private transactions. The gold solidus became the international coin par excellence, accepted from one end of the world to the other, and constituting further proof of Rome’s sovereignty and divine favor.
The gold solidus was the most prestigious coin of the Middle Ages, and became one of the most famous coins in history. In the hands of the Byzantine government it maintained its weight and purity for 700 years, a record for any coinage.