Financial problems appear time and again in the record of the third century. Emperors controlled the minting of gold and silver coinage, and there was a constant temptation to make their resources go further by debasing the currency. The change is most striking in the silver coinage. In Trajan’s day, a silver denarius contained just over ninety percent silver. Under Marcus Aurelius, the percentage of silver as opposed to base metals dropped below seventy-five percent at a time when the empire was ravaged by warfare and disease. Septimius Severus increased army pay and let the silver content of his coins drop to fifty percent. Caracalla introduced a new silver coin, known as the antoninianus and probably worth two denarii, although its weight was only equivalent to one and a half of these coins. This was abandoned under Elagabalus, but reappeared in the joint reign of Balbinus, Pupienus, and Gordian III. By this time the silver content had fallen close to forty percent. Around the middle of the century the decline rapidly accelerated, and was as little as three to four percent silver by the time Aurelian came to power.

From Adrian Goldsworthy’s The Fall of the West: The Slow Death of the Roman Superpower, London: Weidenfeld and Nicolson, 2009, p. 141.