The Follis: Late Rome's Bronze, and the Byzantine Coin It Became

What "follis" actually denotes

Start with the honest difficulty: "follis" is partly a modern label. The word appears in late Roman sources but its precise application to specific coins is uncertain and debated, and numismatists adopted it as a convenient name for two large bronze denominations that bracket late antiquity — the silvered bronze of Diocletian's reform and the M-marked bronze of Byzantium. Treat the term, then, as a useful handle rather than a precise ancient denomination, and the coin stops being confusing. The follis is the bronze spine that runs continuously from the Roman imperial series straight into Byzantine money — there is no break, which is exactly why it matters.

The Diocletianic follis

The first follis is a product of Diocletian's great currency reform of about AD 294, the centrepiece of the Tetrarchic rebuilding of the Roman state. It is a substantial coin — on the order of ten grams at introduction — of bronze with a thin silver wash that gave it a bright surface when new, and its classic reverse is the GENIO POPVLI ROMANI type, the Genius of the Roman People standing with cornucopia and patera. Struck across the whole reformed mint network, from Trier in the west eastward, it is the coin that physically embodies the Tetrarchy's attempt to put Roman money back on a controlled footing after the third-century collapse described in the denarius and aureus guides.

The follis did not stand alone. The Diocletianic reform also struck a laureate fractional bronze (the so-called post-reform radiate, continuing the third-century radiate's look) and a small laureate piece beneath it, so a "follis" is really the top of a short bronze ladder rather than a single coin. Many Tetrarchic folles also carry a value or control formula in the field or exergue — the much-discussed XXI mark among them — whose exact meaning is still debated; treat it, like the coin's name, as a recorded feature to attribute by rather than a settled fact. The point for a collector is that the follis is best learned as a system, not an isolated denomination.

The century of shrinkage

The follis's real story is that the reform did not hold. Across the following decades the coin was repeatedly reduced — lighter, smaller, less silver — so that the large Diocletianic piece becomes the medium bronze of the Constantinian dynasty and then the small AE3 and tiny AE4 of the later fourth century. Watching a GENIO follis of 300 next to a FEL TEMP REPARATIO of the 350s and an illegible AE4 of the 390s is the single best physical lesson in late Roman monetary history: the same denomination lineage, visibly contracting decade by decade. It is also why so much fourth-century bronze is so cheap — it was struck in hundreds of millions of pieces across that whole shrinking sequence.

AE1–AE4: the catalogue problem

This is where collectors get tangled, so it is worth stating plainly. Because the ancient names and exact values of the shrinking fourth-century bronze are uncertain, the standard references — RIC and, following it, the NumisLens catalogue — classify these coins by module size: AE1 (largest) through AE4 (smallest), measured in millimetres rather than named as denominations. So a coin a dealer's listing calls a "follis" will often appear in the reference data as an AE2 or AE3 instead. Neither is wrong; they are answering different questions — the dealer is naming a denomination tradition, the catalogue is recording a measurable fact. Knowing that the two vocabularies coexist is most of what stops follis attribution being frustrating. The practical workflow is simple: measure the diameter and weigh the coin first — that places it on the AE1–AE4 scale — then read the reverse legend and the exergual mint mark to fix the reign and mint. Module size is data, the reverse type is the date, the exergue is the mint; in that order the late Roman bronze stops being a shapeless mass of "small bronzes" and becomes a readable sequence.

The Byzantine follis and the M

The second follis is the one most people picture: the big Byzantine bronze with a giant M on the reverse. It begins with Anastasius I's reform of AD 498, which created a properly organised bronze coinage on a multiple-nummi system. The M is the Greek numeral forty — the coin is a 40-nummi piece — usually over an officina letter, and from Justinian I a regnal year is added, which makes Byzantine folles among the most precisely datable of all ancient coins. The follis sits at the top of a clean Byzantine bronze ladder whose marks a collector should simply memorise: M = 40 nummi (the follis), K = 20 (half-follis), I = 10 (decanummium), E = 5 (pentanummium). Read the value letter, the officina beneath it, the mint in the exergue, and the regnal year beside it, and a Byzantine follis dates itself almost to the year. The series runs for centuries, through the overstruck and increasingly crude folles of the seventh-century crisis — when old coins were simply restruck rather than melted, so two emperors' types can survive on one flan — to the large 10th–11th-century Anonymous folles bearing the bust of Christ and no emperor's name. This is the same denomination idea, reborn: the bridge from late Rome into the full Byzantine coinage is a bronze one, and the follis is the coin that carries it.

Collecting and the market

The coin that defines a follis budget is the late, shrunken bronze, and it costs almost nothing. Common Constantinian-era reduced bronze and ordinary middle-Byzantine folles in respectable grade frequently sit in the low tens of dollars, which makes a long emperor-by-emperor run in big, readable bronze genuinely affordable. Choice large Diocletianic folles with surviving silvering, early dated Justinianic folles, and the popular Anonymous folles in high grade move into the low-to-mid hundreds; the scarcer mints, dates and the finest silvered Tetrarchic pieces higher still. Few denominations let a collector own a coherent five-century story this cheaply — a single follis each from Diocletian, a Constantinian emperor, Anastasius, Justinian I and a tenth-century Anonymous issue sets out the whole arc from late Rome to mature Byzantium in five affordable coins. The companion valuation guide covers reading comparables before buying the better pieces.

Two practical notes. First, original silvering on a Tetrarchic follis is a real and large value factor, and it is also faked — artificial re-silvering is common, so learn what genuine surviving wash looks like. Second, Byzantine folles are frequently overstruck on earlier coins and struck off-centre; that is normal for the series, not damage, but it makes attribution a skill of its own — the regnal year and officina marks are what you read, not the portrait. The follis catalogue facet is the inventory companion to this editorial guide, and the structured NumisLens cabinet records the size-class, mint, officina and date marks that a follis collection actually turns on.

Frequently asked questions

References

1. Sutherland, C. H. V. The Roman Imperial Coinage, Vol. VI (Diocletian's reform). Spink, 1967.
2. Kent, J. P. C. The Roman Imperial Coinage, Vol. VIII. Spink, 1981.
3. Grierson, P. Byzantine Coins. Methuen / University of California Press, 1982; and the Dumbarton Oaks Catalogue.
4. Online Coins of the Roman Empire (OCRE) — the ANS open catalogue.