Reading Roman Bronze: AE1–AE4 Explained

Open any catalogue of fourth- and fifth-century Roman bronze and you will see coins described as Æ1, Æ2, Æ3, or Æ4. New collectors often assume these are denominations, like the sestertius or the as. They are not. 'Æ' is simply the chemical-style abbreviation for aes — bronze — and the number is a measure of the coin's diameter. It is a sizing shorthand that exists because the actual denomination names of the period are genuinely uncertain.

The four size bands

The modules follow rough diameter ranges that have been standard in the literature since the 19th century. They overlap a little at the edges, and dealers sometimes disagree by a millimetre, but the bands are consistent enough to be useful at a glance.

• Æ1 — larger than 25 mm. The big late bronzes; relatively scarce.
• Æ2 — 21 to 25 mm. The 'maiorina' size; includes many popular reform types.
• Æ3 — 17 to 21 mm. The workhorse of the fourth century; most common.
• Æ4 — under 17 mm. The tiny late bronzes, often crudely struck.

Why not just use denomination names?

Because the Roman government reformed its bronze coinage repeatedly, and the ancient names — nummus, follis, centenionalis, maiorina — were attached to different coins at different times as the metal was debased. A 'follis' under Diocletian's reform of 294 was a large silvered bronze; a century later the same word meant something far smaller and baser. Modern scholars cannot always say with confidence which name a given coin carried, so they describe what they can measure: its size. The module system sidesteps an unsolved problem.

Why the size matters for value

All else equal, larger modules are scarcer and more desirable. A crisp Æ1 or a well-struck Æ2 maiorina with full silvering carries a premium over the abundant Æ3 'soldier' types. Module also helps you spot a bargain: a coin sold loosely as a common Æ3 type may actually sit at the large end of its range, or carry an unusually complete strike, which the price may not reflect. Read the diameter the seller lists, compare it to the bands above, and you will quickly develop an eye for which late bronzes are ordinary and which are quietly special.