The denarius was introduced in Rome around 211 BC as a high-quality silver coin. For centuries it was the predominant coin in the empire. However, over time, because of the crisis of the third century, the silver content of the denarius was drastically reduced. By the end of that century, the denarius had practically disappeared as a silver coin and had become a debased bronze coin with only a symbolic silver coating.

When Diocletian came to power, the Roman monetary system was in crisis. Confidence in the denarius had fallen, and the emperor tried to revitalize the economy by introducing new, more stable coins, such as the argenteus (of purer silver) and the follis (a bronze coin coated with silver). These monetary reforms aimed to replace the denarius and restore economic stability.

When Diocletian issued the Edict on Maximum Prices in AD 301, he used the denarius as the unit of account for setting the prices of goods and services. Although the coin had lost much of its value, it was still used as a reference for price calculations. However, this exacerbated some problems related to its devaluation:

1. • Displacement of the denarius: Although the edict used the denarius as a price reference, in practice other coins, such as the follis, were replacing it. The decision to continue using the denarius contributed to confusion in the market, since merchants had less confidence in this coin.
2. • Impracticality of the denarius as a medium of exchange: Although it continued to be used nominally, the loss of value of the denarius made the edict difficult to apply. Merchants did not want to accept debased denarii, preferring to turn to the black market or to more stable coins.
3. • Monetary reforms: Diocletian tried to introduce new coins, such as the argenteus (a purer silver coin) and the follis (a bronze coin coated with silver). The edict represented, de facto, the “last breath” of the denarius, since Diocletian’s monetary reforms tried to establish a more stable system.
4. • Confusion in the economy: Using the degraded denarius as the reference unit in the edict contributed to greater economic confusion, causing many merchants to hide their products or carry out transactions outside the official system.

The use of the denarius as a reference in the edict reflected its decline. The lack of confidence in this coin, which had once been a symbol of stability, showed the need for a deeper reform. After Diocletian’s reign, the denarius was officially replaced by other coins. During the time of Constantine, from AD 306 onward, the denarius had already disappeared from the Roman monetary system, and the solidus, a gold coin, would provide greater stability.

From the mid-third century AD, the Roman Empire faced serious economic problems, including the devaluation of coinage due to the massive issue of coins with less precious metal. Diocletian attempted to control speculation and inflation by setting maximum prices. In the preamble to the edict, he justified the measure in moral terms:

The edict fixed maximum prices for essential products and services in the Empire, from foodstuffs to luxury goods. Prices were established in denarii, and offenders faced severe sanctions, including the death penalty.

• Superior-quality wheat: 100 denarii per modius (approximately 8.75 liters).
• Barley: 60 denarii per modius.
• Oats: 40 denarii per modius.
• Beans: 100 denarii per modius.
• Medium-quality wine: 8 denarii per sextarius (0.5 liters).
• Common wine: 8 denarii per sextarius.
• Egyptian beer: 4 denarii per sextarius.
• Olive oil: 40 denarii per sextarius.
• Milk: 10 denarii per sextarius.
• Honey: 40 denarii per pound.
• Good-quality wheat bread: 2 denarii per pound.
• Beef: 8 denarii per Roman pound (327 grams).
• Pork: 12 denarii per pound.
• Lamb: 6 denarii per pound.
• Large fish: 16 denarii per pound.
• Small fish: 8 denarii per pound.
• Cheese: 24 denarii per pound.
• Eggs: 2 denarii per egg.

• Stone bricks: 150 denarii per 1000.
• Roof tiles: 50 denarii per 100.
• Gypsum: 150 denarii per 1000 pounds.
• Gold: 50,000 denarii per Roman pound.
• Silver: 6,000 denarii per Roman pound.
• Copper: 100 denarii per pound.

• Common wool tunic: 2000 denarii.
• Egyptian linen handkerchief: 100 denarii.
• Embroidered silk tunic: 6000 denarii.
• Leather sandals: 150 denarii.

• Daily wage of a carpenter: 50 denarii per day.
• Agricultural laborer: 25 denarii per day.
• Lawyer: 250 denarii per case.
• Barber: 2 denarii per shave.
• Teacher of grammar and rhetoric (per pupil per month): 250 denarii.
• Specialist physician: 150 denarii per consultation.
• Midwife: 100 denarii per birth.

• Glass cup: 1000 denarii.
• Silver mirror: 5000 denarii.
• Common perfume: 300 denarii per pound.

• Fare for 1 Roman mile in a carriage drawn by 4 horses: 20 denarii.
• Transport by ship of 1 modius of wheat for every 10 nautical miles: 8 denarii.
• Delivery of letters over 100 Roman miles: 150 denarii.

Diocletian made clear in the edict that the sanctions for failing to comply with the regulations would be severe:

“Ut tolerabiliores fiant res omnes populis nostris, pretia statuimus: ne quis inhumana cupiditate pecuniae calcare videatur humanas necessitates.”
(Translation: “To make all things more tolerable for our peoples, we have fixed prices: so that no one, with an inhuman desire for money, may seem to trample upon human needs.”)

Despite Diocletian’s intentions, the edict failed. The Roman economy was too complex to be controlled through fixed prices, which led to an increase in the black market. Merchants hid their products or carried out transactions outside the official system.

Although it failed in its application, it remains an important example of the challenge of managing a centralized economy. The denarius, which had been key to the Roman economy for centuries, became obsolete after this period and was replaced by more stable coins, such as the gold solidus.

During Diocletian’s reign, the Roman monetary system was reorganized to halt inflation and restore confidence in coinage. Coins such as the aureus and the argenteus remained benchmarks of stability in gold and silver, while the follis was introduced to meet the need for a more widely circulating everyday coin. Other coins, such as the antoninianus and the denarius, had been debased or eliminated and no longer played an important role in the Roman economy of the period.

Diocletian’s aureus was a pure gold coin, weighing approximately 5.45 grams and with a purity close to 99%. Although it had already been used before his reign, Diocletian maintained and adjusted the aureus in his reformed monetary system in order to stabilize an economy that had suffered decades of inflation and devaluation.

The argenteus was a silver coin with a purity of 95 to 97%. It was designed to be reliable and solid, in contrast to the denarius, which by that time had suffered a severe degradation in its silver content.

The follis was a bronze coin with a small amount of silver on the surface (a very thin coating), representing between 4% and 5% of its total weight. This silver layer was very superficial, giving the coin a silvery shine at first, although it quickly wore away with use.