One of the more troublesome aspects of the Castle Zagyg campaign setting is that its economy seems to exist in isolation from both that of Dungeons & Dragons (any iteration) and Castles & Crusades. As I understand it, the underlying reason for this was that Gygax approached the design and development of Yggsburgh from the point of view of his Lejendary Adventure system and Fantasy Worlds series, which is to say he used nonstandard terminology for the equipment lists and assessed everything in dollars. The issue was further problematised during editing by the erroneous conversion of dollars to gold coins at a rate twenty-five times that intended, and the smoothing over of any resulting inconsistencies. So, for example, a long sword at Elite Arms & Armour is valued at 4,200 gold pieces in the Yggsburgh campaign setting book, but was supposed to cost only 168 gold pieces (or $3,360 in the original manuscript). This compares quite disproportionately with Castles & Crusades and Advanced Dungeons & Dragons, where a long sword costs a mere 15 gold pieces, but it is perhaps an unfair comparison given that hafted weapons at the same location cost generally less than 2 gold pieces at the correct price (that is less than $40 in the original manuscript).
At first it seemed simply a matter of going through the text and correcting the numbers, as the conversion error was apparently consistently applied throughout. However, because the setting book was only meant to be a starting point, it being expected that the game master would add detail either from his own imagination or using the then projected twelve town expansions, some frame of reference is necessary, and neither the listed prices in Gary Gygax’s World Builder, nor those in the Castles & Crusades or Dungeons & Dragons rulebooks, accord with what is found in Yggsburgh. Frustratingly, the town expansions that did see publication refer the reader to the Castles & Crusades equipment lists, which even after a degree of conversion are wholly unsuitable. The only really viable solutions are to either discard the Castle Zagyg price lists in favour of those of another system, or else to attempt some sort of integration. Whichever of these is attempted, it is first desirable to correct all of the erroneous calculations in the Yggsburgh text in order to get an idea of what the original manuscript intended; having had cause to do so myself I have made the results available for download here.
Whatever his ability as a game designer and author, numismatics appears to have been of only passing interest to Gygax. The exchange rates of gold to silver he provided for the Castle Zagyg campaign setting are the same as those that appear in his Fantasy Worlds series, and according to those volumes are based on renaissance exchange rates. Unfortunately, there is little to support this assertion, possibly his understanding of inflation and coinage for that period was flawed, but it is also notable that the ratio looks very similar to the contemporary market at the time of writing (about 50:1 silver to gold), which may have influenced his thinking. As with Dungeons & Dragons, Gygax envisioned the “gold piece” of Yggsburgh to be quite heavy (437.5 grains) by comparison with medieval coins, perhaps modelling them on the extremely rare late fifteenth century gold double sovereign (480 grains), the more well known silver guldengroschen (491 grains), or the sixteenth century silver thaler (450 grains). He also suggests that smaller coins might circulate, perhaps worth a half or a tenth of a gold piece, which rather makes one wish he had stuck more consistently to decimals for the purposes of game play.
It is worth noting at this point that several different exchange rates and coin weights have been used in Dungeons & Dragons. The original game (1974) used a 1:10:50 ratio of gold to silver to copper, whilst Advanced Dungeons & Dragons (1979) used a 1:20:200 ratio. It was not until the Moldvay edition of Dungeons & Dragons (1981) that the more straightforward 1:10:100 ratio was adopted, which was rather sensibly embraced for the second edition of the advanced game (1989) and later for D20/3e. Encumbrance was originally measured in coins, and it was strongly implied that one coin was equal to a tenth of a pound (700 grains), even though also stated that the measurement encompassed bulk as well as weight. When second edition switched to using pounds directly as the measure of encumbrance the weight of the standard coin was also set at a fiftieth of a pound (140 grains), accompanied by a brief and somewhat inaccurate overview of ancient and medieval monetary systems. These largish coins would be roughly equivalent in size to the ancient stater, tetradrachm, or aureus, which would in turn be roughly twice the size of the drachme, denarius, or solidus. A brief and incomplete overview is available for download here.
The fact of the matter is that ancient and medieval coins could come in extremely variable sizes and denominations, not to mention purity. Whilst a weight of 1-10 grams seems to have been the most common range for coins intended for circulation, the gold piece need not be regarded as anything more than a unit of account, which is how the dollar is treated in the Lejendary Adventure system. Exchange rates are less readily dealt with; although a 1:20 gold to silver ratio is not entirely unreasonable, a 1:50 ratio seems faintly ridiculous for any setting looking to evoke the ancient or medieval world. As a compromise between verisimilitude, aesthetics, and simplicity of play the 1:10:100 ratio seems the most suitable. In the same spirit, the default coin would be best fixed at either ten or one-hundred to the pound. That ten to the pound is probably unsuitable is evident from a brief survey of the jewellery and other items of precious metal that appear in prominent Dungeons & Dragons modules. As early as G1 Steading of the Hill Giant Chief we are faced with a belt buckle (albeit giant sized) specified as containing one-hundred gold pieces worth of gold (ten pounds) and a large golden hairpin worth five-hundred gold pieces (fifty pounds).
None of the above is intended to invalidate any given approach to coinage in the East Mark or swords & sorcery adventure games more generally, but rather represents a short exploration of the relationship between the value and weight of precious metals in Dungeons & Dragons. Gygax famously noted in the Player's Handbook that the prices quoted reflected a “boom town” economy, the idea being that large amounts of treasure liberated from a dungeon would drive up prices locally. In fact, though, even relative costs are highly variable in the game system, some things are simply over or under priced for whatever reason, and the frequent appearance of multiples of “100 GP” are suspicious. The disparities have led some to suppose that there may be two economies reflected in the game, one “big” and intended for adventurers and the other “small” and representing more normative costs. When the wages of a captain outstrip that of the total for his entire company it is hard not to notice these issues, and yet one supposes these were interlinked design choices. At any rate, it is neither a relationship Gygax perpetuated for his Castle Zagyg campaign setting, nor a precedent I propose to emulate.