Coins of the 4th Century AD

Changes in Roman bronze coinage of the 4th Century AD
The antoninianus (215-294 AD)‎
During and leading up to the 4th century AD, we see many instances of reform to the coinage of ‎the Roman Empire. One particularly important change was the discontinuation of the ‘silver’ ‎‎(radiate) antoninianus denomination by Diocletian in 294 AD, to be replaced by silver-free "post-‎reform radiates", which finally found disuse in the west by about 299 and in the east by 307.‎
The Follis (‘large’ 294-306 reduced nummus 306-byzantine era)‎
During the same 294 AD coinage reform in which the antoninianus denomination found its ‎demise, we see the issue of a new denomination known as "surface silver enriched" follis coins ‎‎(these were likely referred to as 'nummus' as we now know that follis the word for a bag of ‎coins). At first, these coins held the same silver content as late pre-reform antoninianus coins ‎‎(about 4%) and had a weight of around 10 grams. This denomination saw a steady reduction in ‎size and silver content over the years. During the early years of Constantine reign as caesar in the ‎west, the weight of this denomination was reduced in London, Lugdunum and Treveri and then ‎again across most of the Empire to 4.4 grams by 307 AD. By 313 AD, a decision by both ‎Constantine and Licinius reduced the size of the follis to 18-20 mm with a weight of 3.1 grams. ‎This module design survived until 330 AD, when it was yet again reduced to 17mm and a weight ‎of 1.9 grams. In 336 AD, we see a final weight reduction of Constantine to the now heavily ‎reduced ‘follis’ coin, which now weighed 1.3-1.6 grams and could be found to have a diameter ‎under 17mm. In order to curb the rampant reduction in the denomination of the follis, Constans ‎and Constantius II made attempts between 320 and 340 AD to introduce a larger denomination ‎which was now known as the bronze centenionali. By the reform of Constantius II in 346 AD, a ‎‎‘double centenionali’ known as a Pecunia maiorina was introduced. These two coins had the sizes ‎and weights of 21-24mm/5.45g and 17-20mm/2.7g respectively. The size of the smaller ‎centenionali lasted until the reign of Theodosius I whereas the Pecunia maiorina was de-‎monetised by an edict in 354 AD. These reduction in the size, weight and silver content of the ‎follis coin during the 4th & 5th centuries directly reflect the inflationary pressures afflicting the ‎empire which had had a devastating effect on the economy during the 3rd Century AD. By the ‎early 5th century, small bronze coins known as Nummi Minimi were being issued at under 11mm ‎and 1.2g at an average exchange rate of 7200 to a single gold gold solidus coin.‎

Classification by Diameter
AE1 from 25 mm
AE2 from 21 mm
AE3 from 17 mm
AE4 under 17 mm