Introduction: Numismatic terminology can be confusing, especially for those new to ancient coin collecting. Part of the difficulty stems from the fact that the terminology in use arises out of a centuries long tradition of studying and writing about coins. Another part of the difficulty is that we truly don't know the names of certain denominations in use in antiquity, particularly the names of the coins of the Roman imperial period after Constantine I. Therefore, our terminology is a mixture of traditional and modern terms, and often there are two (or more) words for the same denomination. This is not an essay about the various denominations. What follows is a discussion of how certain terms pertaining to copper and copper-alloy coins came into being and how we use them today. What's up with the word brass? Ancient coins are made out of copper, orichalcum, or bronze. Why such terms as "first brass" or "second brass" when some of these coins aren't even made out of that alloy? Brass is an old English colloquial term for any copper-based coin. When it first came into use in the medieval period, the word did not specifically refer to an alloy of copper and zinc. Langland, in Piers Plowman, circa 1362 (iii, 188-189), has "pore Men þou robbest, and beere heor bras on þi Bac to Caleys to sulle." This is translated as "You rob poor men, and bear their brass on your back to sell in Calais." In his translation of the New Testament in 1526, Tyndale translates the Greek of Matthew 10:9, Μὴ κτήσησθε χρυσὸν μηδὲ ἄργυρον μηδὲ χαλκὸν εἰς τὰς ζώνας ὑμῶν, as "Posses not golde nor silver nor brasse yn youre gerdels." The Greek χαλκός (chalkos) properly means copper or bronze. The word ὀρείχαλκος (oreichalkos; Latin orichalcum) was used to refer to what we would term brass in the modern sense. But Tyndale used "brasse" because the word denoted any copper coin to Englishmen at the time. At a later period, the word became slang or dialect for money in general. For example: "Shame that the Muses should be bought and sold, For euerie peasants brasse, on each scaffold." -- Bishop Hall, Satires, 1597. "Brass, cur? Thou damned and luxurious mountain goat, offer’st me brass?" -- Shakespeare, King Henry the Fifth (iv. 4), 1599. "Who ne'er despises books that bring him brass." -- Byron, Hints from Horace (548), 1811. So that's why the term "brass" is sometimes used in numismatics to refer to coins that are made of copper or bronze, in addition to those made of orichalcum. First brass, second brass, and all that jazz: The terms first, second, third and fourth brass do not refer to specific denominations, but are terms used to denote the size of coins. This terminology dates to the renaissance, when people didn't have standardized units of measurements nor were rulers or calipers in widespread use. The term "inch," for example, varied quite literally from place to place and reporting a coin's diameter objectively was not feasible. Early numismatic terminology reflects this. "First brass" refers to the largest coins, "second brass" to the second largest coins, "third brass" to the third largest coins, and "fourth brass to the fourth largest (the smallest) coins. Early numismatists used the abbreviations Æ I, Æ II, Æ III and Æ IV to refer to these four sizes. Copper-alloy coins of the Roman Principate, i.e. pagan Rome (31 BC-AD 296), came in three sizes, large, middle, and small and "first," "second," and "third brass" (Æ I-Æ III) were used to describe these coins. Indeed, the term "middle bronze" is still used to this day to describe coins of the as or dupondius denominations, especially when patina obscures their metallic composition and it's unclear which denomination they may be. An illustration from @dougsmit 's educational website depicts these three sizes. Sestertii are first brass sized, dupondii and asses are second brass sized, and semisses and quandrantes are third brass sized: The term "first brass" refers to any coin that is sestertius-sized, more than about 26 mm in diameter. Banduri, writing in 1718, for example, lists the sestertii of Trajan Decius under a section titled "Numismata Latina Æ. I.", meaning "Roman coins, first brass": But he also uses the term Æ I to also refer to Roman colonial issues ... ... and to Roman provincial coins in the Greek language, which he refers to as "Greek coins first brass": Similarly, Banduri uses Æ II to refer to dupondii and asses ... ... and also to Roman provincials of similar size: Lastly, he uses the term Æ III to refer to semisses and quadrantes, Roman colonial and provincial coins of similar size, as well as to the tiniest late Roman bronze coins of only a centimeter in dimension (more about this later): Wiczay, writing in 1814, uses the same terminology as Banduri, but he uses the term Æ IV to refer to the tiniest of coins. Here is his listing for coins of Marcus Aurelius: Note Wiczay's use of Roman numerals I and II to describe these coins. No. 1459, for example, is a sestertius (I), with a portrait he describes as "Cap. laur.," an abbreviation for "laureate head." No. 1457 is a dupondius (II), with a portrait he describes as "cap. rad. min.," an abbreviation for "radiate head, smaller." Cohen, writing in 1880, does not use the modern terms "sestertius," "dupondius," "as," "quandrans," etc., either. Rather, he simply uses the terms GB, MB, and PB, to refer to grande (large), moyenne (medium), and petit (small) copper alloy coins. No. 16, a PB (small bronze) has no S C on the reverse and is the CERERI FRVGIF type used for the denarius (no. 15). This listing can only refer to a limes denarius, described as PB because it's the size of a semis or quadrans. No. 18 is a GB (large bronze, i.e. sestertius) with the CERES S C reverse, while no. 19 is the same design, but a MB (middle bronze, i.e. as or dupondius). For coins of the Roman principate, including colonial and provincial issues, we no longer use the terms "first brass," "large bronze," or Æ I; "second brass" or Æ II (though we still use "middle bronze" when a coin cannot be determined to be an as or dupondius); or "third brass," "small bronze," or Æ III. Rather, we use the name of the denomination when known, such as "sestertius," "quadrans," or "tetrassarion." For provincial coins whose denomination is not known, we use Æ (an abbreviation for aes) plus the diameter in millimeters, such as Æ 24 or Æ 18. More follows ... ~~~ 1. Bandurius, Anselmus. Numismata Imperatorum Romanorum a Trajano Decio Ad Palaeologos Augustos. Vol. 1, Montalant, 1718. Available online here: Vol. 1, Vol 2. 2. Wiczay, Michael A. and Felice Caronni. Musei Hedervarii in Hungaria numos antiquos graecos et latinos descripsit. Vol. 2, Caronni, Vienna 1814. Available online here. 3. Cohen, Henry. Description historique des monnaies frappées sous l'Empire Romain, Tome IV: de Septime Sévère à Maxime (193 à 238 après J.-C.). Paris, 1880, p. 107.