Follis
Moneta Historical Research by Tom Schroer
"Follis" (plural: folles) is a Latin word which meant a leather bag, and in particular referred to a money-pouch. The large billon of Diocletian's 294 reform were distributed in large leather bags and hence came to be known as folles.
The sweeping reform of 294 re-established silver coinage with the advent of the "argenteus", and the antoninianus was discontinued (along with the vestigial issues of denarii, Ar quinarii, and bronzes). In the place of the antoninianus and the rarely-used bronze denominations were issued three new denominations, one base billon and two bronze. The base billon (4% silver) coins were the folles. Folles always carried a laureate or helmeted bust, except for posthumous issues, which could be bare-headed or veiled. The two bronze denominations became known as "post-reform radiates" from the radiate bust which they always carried, and Ae denarii (laureate bust coins of about 1.4 grams).
The follis was originally struck at a weight between 8.5 and 11.0 grams (most between 9 and 10.5), and a theoretical weight of 32 to the pound (10.23 grams) has been suggested. C.H.V. Sutherland in Roman Imperial Coins Volume VI makes a convincing case that the follis was tariffed at 5 "denarii communes" (common denarii, today generally known as Ae denarii), or 1/5 of an argenteus (q.v.). He suggests that the radiate was tariffed at 2 Ae denarii. The appearance of the mark "XXI" in the exergue of folles of Siscia and the field of folles of Alexandria about 300 (originally introduced by Aurelian on antoniniani) has been interpreted to mean that the follis (and late antoninianus) was equal to 20 sestertii, although that meaning is not certain. Indeed the "XXI" mark has also been held to mean that the coins contained 20 parts copper ro 1 part silver, but the appearance of "KV" on folles of Antioch of 300 supports the theory that the meaning is 20 sestertii, or five of the "denarii communes". (Thus the pieces of Tacitus, Carus, and Carinus which carry the marks "I.A", "X.I", "X.I.I", and "X.ET.I" may have been a reform effort aimed at lowering the value of the debased antoninianii.)
The weight of the follis was held rather constant until early 307 when Constantine I reduced it to from 6.0 to 7.0 grams, and he reduced it again in 310 to a weight of between 4.0 and 5.0 grams. The silver content of the follis was reduced to around 2% at about the same time as Constantine's first weight reduction. The follis gradually declined to about 3.5 grams before it gave way to the "centenionalis". Even though the follis was shrinking in silver content and weight, it may have been re-valued upward about 312 to 25 "denarii communes" to take the place of the argenteus, which was temporarily suspended from production.
The follis was not officially discontinued at any point in time, rather it continued to shrink slowly until it was simply unrecognizable. At some point before 348 the name "centenionalis" began to be used, although common modern practice is to begin using the terms "Ae3" and "Ae4" for coins after about 318, the introduction of the "VICTORIAE LAETAE PRINC PERP" type which was probably re-tariffed at 12.5 "denarii communes".
The earliest folles were 27-30 millimeters in diameter, falling to 23-25 millimeters with the first weight reduction in 307, and to 21-23 millimeters with the second reduction in 310. After the defeat of Maximinus II (q.v.) in 313 they were reduced yet again to a diameter of about 18-19 millimeters, where they remained until the nominal end of the denomination about 318.
Follis of the Tetrarchy A.D. 293 - 306
In 293, Diocletian introduced the follis (plural: folles) a new larger denomination with a laureate portrait to replace the radiate antoninianus (or aurelianianus). Diocletian 's new denomination had a copper core, and a 5% silver plate, the same as the radiates it replaced, but was c. 28 - 32 mm diameter, on a consistent weight standard of 10.75 grams. The follis was initially tariffed at 5 denarii communes (also the same as the radiates it replaced), but was later devalued to 12.5 d.c. and then to 25 d.c. Smaller fraction were struck with a radiate portrait, called "post-reform radiates." On the tetrarchic folles, portraits of the various emperors were highly stylized and usually indistinguishable. Often the emperor depicted can only be determined by the obverse legend. The most common reverse type had the legend GENIO POPVLI ROMANI, and depicted the Genius (spirit) of the Roman people standing making a sacrifice. In 301, the western mints struck a common type with the legend Sacra Moneta, and depicting Moneta standing holding scales and a cornucopia. The large folles of the Tetrarchy fell out of circulation in 306 when weight standards were reduced.
Byzantine Follis
In the Byzantine period, the follis was the largest denomination of copper coin, initially worth 40 nummi.