The coins of the Roman Republic prior to 241 BC are rare and expensive and therefore unlikely to appear on this website. However, for completeness, a rough chronology is listed below.
280-241 BC: Small numbers of gold coins.
280-211 BC: So-called "pre-denarius" silver coins based on those of Magna Graecia (the Greek colonies within Italy).
5th-4th centuries BC: "Aes Rude" - irregular lumps of bronze.
289-241 BC: "Aes Signatum" -large cast stamped ingots of bronze.
280-211 BC: "Aes Grave" - large cast bronze coins.
217-211 BC: "Aes Grave" -large struck bronze coins.
Finally in 211 BC the Aes Grave coinage was reformed and became a more recognizably bronze struck coinage, based on an "As".
Also in 211 BC, the basic silver unit of a denarius came into being, originally valued at 10 asses, later re-tariffed to 16 asses.
At the start of the Imperial period, around 18 BC, Augustus re-organized the currency system, including re-introducing a gold coinage. This was to last almost three centuries.
During the Imperial period, silver coins were struck in the Greek part of the Empire, based on the pre-existing coins, drachms and tetradrachms. Some cities (not just Greek) were also allowed to strike their own bronze coins, with or without inscriptions acknowledging imperial rule. Both types of coins are known as 'provincial' or Greek imperial'.
From the end of the first century, the denarius, the principal silver coin of the Empire was gradually de-based.
Around 215 AD, Caracalla (Antoninus) introduced a new silver coin, one and a half times the weight of the denarius and believed to be worth two denarii. One reason it is believed to be a two denarii coin is that the emperor's bust is wearing a radiate crown, often an indication that a coin is worth twice another (as with the dupondius which was worth 2 asses). If it had a special name it is not known and today is called an Antoninianus after Caracalla.
However, the coinage continued to be de-based and reduced in size. Aurelian (270-275 AD) reformed the coinage producing a new improved antoninianus. These coins often had the mark "XXI" on the reverse, believed to refer to the metal content of twenty parts of base metal to one of silver. They may have been double the value of the old antoniniani but whether this was so is not known.
Aurelian's reforms seem to have been unsuccessful and Diocletian (284-305 AD) in 294 AD replaced the coinage with a complete new set of coins. The principal base metal coin is known (without justification) as a Follis. This was a large coin (initially around 12 grams) and contained a few per cent silver and was silvered on the outside. There were also a number of smaller bronze coins, perhaps associated with the change-over from the old coins. He also issued a pure silver coin known as an Argenteus (again without justification). This was the same weight and size of the old Denarius back in it's hey-day.
The last volume of David Sear's five volume "Roman Coins and their Values" (RCVM) was published at the end of 2014. Whilst the arrangement and relative values of Diocletian's coinage, and indeed of all the coinage thereafter until the fifth century, remains speculative, RCVM now groups likely denominations together and provides the nominal weight of each likely grouping. This has allowed me to display my late Roman coins on this website in denominational order (as far as is possible) with nominal weights alongside actual weights.
The table below shows the possible arrangement of the coinage after Diocletian's reform.
Reforms of Constantine and after
See table below
In 310 A.D., Constantine, who was sharing the Empire with Licinius, introduced three new gold coins. The first was the Solidus. This weighed 1/72 of a Roman Pound, as opposed to 1/60 for the Aureus. It was to be the main coin of choice (for the richer people) for the Empire, right through to the Byzantine Empire and beyond. The second was a Semissis or half Solidus was
The third gold coin Constantine introduced is known today as a 'One and a Half Scrupulum' (A Scrupulum was a unit of weight, there being 288 of them to the Roman Pound). This coin was lighter than the other two and we might expect it to have been a worth third of a Solidus. But it wasn't. Modern writers tentatively call it 9 silver Siliquae or Argentei (see section below for the these silver coins). However, if the relative bullion values of gold and silver changed over time, which they probably did, that relationship would no longer be valid. I prefer to think of the coin as being one third of an Aureus, even though it is slightly light (1.7 grams versus 1.8 grams). It was eventually replaced by the Tremissis or one third of a Solidus, although not for some 70 odd years.
There were several multiples of Solidi which were infrequently minted over the years. A Semissis or half Solidus was introduced around 317. The Aureus continued to be minted sporadically well into the 5th century. Supposed the Aureus was produced for use in the East, but it appears to have been minted in Eastern and Western mints. However, only the Solidus and it's fractions were in general use. The rest were donatives, minted on special occasions.
See table below
Production of Diocletian's silver Argenteus was reduced after 305 and was eventually halted.
By 325 Constantine had seen off Licinius and was master of the entire Roman Empire, helped by his sons. At that time he introduced two new silver coins. Or rather he introduce one and re-introduced another. The re-introduced one is today called the Siliqua. This coin is in fact the same weight and size as Diocletian's Argenteus, which in turn is the same weight and size as the Denarius of a couple of centuries before.
The other coin is (or was?) called a Miliarensis. This odd denomination nominally weighed 4.5 grams, compared with 3.34 grams for the Siliqua. That made the Miliarensis worth, bizzarely, one and a third Siliquae. To avoid confusion (and there is a lot to be confused about) we should call these coins the heavy Siliqua and the light Miliarensis, because around 338, Constantine's sons introduced a 'heavy' Miliarensis. Although it was not until 357, a 'light' or reduced Siliqua was introduced which for some time circulated alongside the 'heavy' Siliqua. Just before the introduction of the 'heavy' Miliarensis, a silver multiple was produced having a weight four times that of the Siliqua. The weights of all these different denominations are shown in the table below. Note that the Siliqua is given a nominal value of 10 so that no decimal numbers are produced. The weights seem to have been deliberately chosen. It's not a case of de-basement as happened with the Denarius. The weights seem to divide up into an 'aureus' system, with the 'heavy' Miliarensis weighing the same as the Aureus and a 'solidus' system with the 'light' Miliarensis weighing the same as the Solidus. The other denominations form an interesting, if unexplained, pattern of weights. Probably the relative values of gold and silver bullion changed over time and that this was any easy way of converting by weight.
However, most of these denominations continued to be issued over the years, but rarely and in small numbers, apart from the Siliqua. The higher value silver coins seem to have been given as donatives and are quite rare today.
(billon means a mixture of bronze with a small amount of silver)
The Follis rapidly declined in size and weight after the abdication of Diocletian. By 325, the other billon/bronze denominations had disappeared, leaving only a lightweight billon Follis, now known as a Centenionalis.
It was not until 348 that Constantius II introduced a new set of coins. These are known as today, based partly on the use of the word maiorina in contemporary texts, as a 'heavy' Maiorina, 'light' Maiorina (there are those words 'heavy' and 'light' again), Half Maiorina and Quarter Maiorina. The quarter was bronze, the rest billon. They were marked 'FEL TEMP REPARATIO' or 'good times are back again'.
These new denominations lasted no more than six years. Julian the Apostate produced his large famous large pagan 'bull' coins which were made of billon. But apart from that the coinage now consisted of mainly small bronze issues.
Undoubtedly the value of the bronze and billon coinage of the late Roman Empire changed with respect to gold and silver, invariably downwards. Put another way, if you had wanted to exchange your bronze coins for silver or gold ones, you had to buy them at the current bullion value. So it is probably fruitless to look for a 'value' for these late bronze coins apart from 'the big coin is worth x times more than the small coin'.