quality:correction, information:extraction
Currency and inflation

Aurelian's attempt to reform the currency had failed; the denarius was dead. Diocletian restored the three-metal coinage and issued better quality pieces. The new system consisted of five coins: the aureus / solidus, a gold coin weighing, like its predecessors, one-sixtieth of a pound; the argenteus, a coin weighing one ninety-sixth of a pound and containing ninety-five percent pure silver; the follis, sometimes referred to as the laureatus A, which is a copper coin with added silver struck at the rate of thirty-two to the pound; the radiatus, a small copper coin struck at the rate of 108 to the pound, with no added silver; and a coin known today as the laureatus B, a smaller copper coin struck at the rate of 192 to the pound. Since the nominal values of these new issues were lower than their intrinsic worth as metals, the state was minting these coins at a loss. This practice could be sustained only by requisitioning precious metals from private citizens in exchange for state-minted coin (of a far lower value than the price of the precious metals requisitioned).

By 301, the system was in trouble, strained by a new bout of inflation. Diocletian, therefore, issued his Edict on Coinage, an act re-tariffing all debts so that the nummus, the most common coin in circulation, would be worth half as much. In the edict, preserved in an inscription from the city of Aphrodisias in Caria (near Geyre, Turkey), it was declared that all debts contracted before 1 September 301 must be repaid at the old standards, while all debts contracted after that date would be repaid at the new standards. It appears that the edict was made in an attempt to preserve the current price of gold and to keep the Empire's coinage on silver, Rome's traditional metal currency. This edict risked giving further momentum to inflationary trends, as had happened after Aurelian's currency reforms. The government's response was to issue a price freeze.

The Edict on Maximum Prices (Edictum De Pretiis Rerum Venalium) was issued two to three months after the coinage edict, somewhere between 20 November and 10 December 301. The best-preserved Latin inscription surviving from the Greek East, the edict survives in many versions, on materials as varied as wood, papyrus, and stone. In the edict, Diocletian declared that the current pricing crisis resulted from the unchecked greed of merchants, and had resulted in turmoil for the mass of common citizens. The language of the edict calls on the people's memory of their benevolent leaders, and exhorts them to enforce the provisions of the edict, thereby restoring perfection to the world. The edict goes on to list in detail over one thousand goods and accompanying retail prices not to be exceeded. Penalties are laid out for various pricing transgressions.

In the most basic terms, the edict was ignorant of the law of supply and demand: it ignored the fact that prices might vary from region to region according to product availability, and it ignored the impact of transportation costs in the retail price of goods. In the judgment of the historian David Potter, the edict was "an act of economic lunacy". The fact that the edict began with a long rhetorical preamble betrays at the same time a moralizing stance as well as a weak grasp of economics – perhaps simply the wishful thinking that criminalizing a practice was enough to stop it. There is no consensus about how effectively the edict was enforced.

Supposedly, inflation, speculation, and monetary instability continued, and a black market arose to trade in goods forced out of official markets. The edict's penalties were applied unevenly across the empire (some scholars believe they were applied only in Diocletian's domains), widely resisted, and eventually dropped, perhaps within a year of the edict's issue. Lactantius has written of the perverse accompaniments to the edict; of goods withdrawn from the market, of brawls over minute variations in price, of the deaths that came when its provisions were enforced. His account may be true, but it seems to modern historians exaggerated and hyperbolic, and the impact of the law is recorded in no other ancient source.