This coin is both "common" and "rare," each in its own way. This coin which arrived yesterday illustrates the point. Constantius I. Augustus of the second tetrarchy, 305-306. 29-27 mm. 8.74 grams. FIDES MILITVM AVGG ET CAESS NN, Fides seated left, holding standard in each hand AQS in exergue RIC VI Aquileia 62, page 320. "C" RIC says this is "common," so how can it be rare? Here is how. Pay attention to the distinction between "types" and "varieties." Different designs get different RIC numbers. Every change in obverse legend gets a new RIC number. Different mints have different RIC numbers. Every change in control mark gets a new RIC number (different officina numbers do not). RIC assigns rarities to individual RIC numbers which are detailed in a way most collectors would call "varieties" rather than "types," where a "type" is determined by the reverse design and legend, not counting mintmarks or control marks. Mintmarks and control marks make "varieties" and distinct RIC numbers. That means a single reverse type can be associated with many RIC numbers, sometimes several at a given mint and from a dozen mints (RIC VI covers 16 mints, not all in operation all the time). So it is easy to see a type can be common and a variety rare. Sellers often say a coin of a common type is "rare" by citing its RIC-number variety rarity as opposed to its type rarity. The case above is not that case; it is the inverse--the variety is "common" but the type rare. A particular variety is, by RIC's definition, "common" by being in every major national collection. This does not necessarily imply very many of that exact variety are known. And, if a type is issued at only one mint for a short period of time and quite rare with only one or two varieties, it is possible that the type is rare yet major museums all have one of that variety (after all, the collectors who donated their coins to the museums sought unusual types). So, the variety can be "common," but there are so few varieties that the type is rare. According to RIC VI, the precise Constantius variety above is in the major museums. But the legend was issued only at Aquileia (not a dozen mints like most follis types of the period). Furthermore, the legend is more often accompanied by Fides standing, whereas this one is seated. Failmezger's excellent book "Roman Bronze Coins: From Paganism to Christianity, 294-364 A.D." lists all the coins by type (not by variety). His Type 44 has the legend and Fides standing. This type with Fides seated is not noted. RIC VI has 727 pages and you can imagine how easy it would be to overlook the distinction between "stg." and "seated" on a rare type listed at only one mint. This type is rare, although glancing at its number in RIC would show "Common". By the way, there are no coins of this type (for any emperor) on vcoins or MA-Shops as I write. Can you show us something related? Maybe a type that is rare but the RIC variety is not?