Generally, lands near each other, sharing a common group of people or a common language have very similar economies. The countries of medieval Europe traded with each other regularly and so developed very similar coins and values. Kingdoms also tend to imitate the economy of the most powerful country in the region. The Byzantine Empire had a stable gold currency, and its coins were the model for rulers from Baghdad to Denmark.
The value of a foreign coin was based on the weight of the coin, but also on the power of the issuer. The Byzantine besant was not only limited by other lands, but it was highly valued in trade. An English merchant would accept these coins from a Venetian trader because he knew their value. His price might increase if the trader paid him in Persian dinars. To the merchant, the dinar was simply not as valuable as the besant.
You can add color to your campaign by choosing to have different systems of trade in different lands. By creating different currencies and ways of trading, you make your players aware of the different kingdoms in your fantasy campaign. This makes them pay attention and learn about your world. A traveling merchant who trades in besants becomes a wealthy trader from the rich lands of Byzantium, while one who deals in hacksilver is a northerner from the cold shores of Scandinavia. These names and places create images, images more compelling and exciting than those created by the plain words "merchant" or "trader."
Types of Coins
The terms "gold piece" (gp), "silver piece" (sp), and "copper piece" (cp) are clear and they are used throughout these game rules. But you can spice them up a bit. People give coins names, whether as plain as "dime" or lively as "gold double-eagle." The imaginary population of a fantasy world should be no different. Medieval history is filled with different types of coinage, all of which can add local color to your campaign.
Take, for example, the situation of a mercenary captain in Aquitaine. Through wages, booty, and trading he has assembled quite a few coins. Foremost of his horde are the gold and silver coins of Byzantium—the besant, hyperpyron, or nomisma as they were known at different times. An Italian general paid him in coins almost equally valuable, the gold florin and ducat. Mixed in with these were other coins of the Italian states—silver grossi and ecu. From the French he collected gros tournois, Rouen pennies, and louis. A Moorish hostage bought his freedom with silver drachmas and a German merchant of the Hanse paid the heavy toll of a gold mark. Part of the spoils of war include solidus aureus and denarii of Ancient Rome, though these coins are so badly worn their value has dropped greatly.
One of his men even came across a horde of hacksilver bracelets! Finally, from his English employers he received pounds, shillings, and pence. Clearly the captain is faced with a problem when he tries to figure out just how much money he has. What do these coins add up to?
The besant, hyperpyron, and nomisma were the standard coins of the Byzantine Empire. They were of a regular size and the precious metal was not debased with lead or copper. Backed by the power of the Emperor, each coin had a steady value. In your game, you could establish their value at one or two gold pieces each.
The florin and the ducat were the coins of different Italian states. These lands, rising in trading power, needed a steady economy. Thus their coins were almost the equal of the besant and were used for trade throughout Europe. Each florin might be equal to a gold piece. The gross was a silver penny and, normally, 12 equalled one florin.
The coins of France were much like those of Italy and could be valued the same way. The louis and the sous were the equal of the florin while the gros tournis and the denarius were silver pennies. However, the Rouen penny was specially minted and not considered as valuable by most traders.
The Middle Eastern drachma was modeled on the besant. Normally 12 to 20 were equal to a single besant (6-10 would equal one gp) but in Aquitaine they were often valued just like other silver pennies. The gold mark wasn't so much a coin as a measure. It was normally figured to be worth six English pounds. There were also silver marks worth about 13 shillings, and Scandinavian ora worth 16 pence. But the true value of these coins was what you could get for them.
The English coins included the rarely seen pound, equal perhaps to one gp. More common were silver shillings, officially figured at 20 to a pound (or half a sp). Below the shilling was the pence, 12 to a shilling, and below the pence was the farthing, four to a pence. Meanwhile, the lowly Rouen penny was figured to be equal to half a pence.
Of the ancient coins, the Roman solidus aureus was the model for the besant and thus nearly all other coins. It in turn was divided into silver denarii with 12 to 40 equaling a single solidus. However, age and counterfeiters reduced the value of these coins so much that their only true worth could be found in what they weighed. During the same time, Scandinavians used hacksilver—silver jewelry. When they needed to pay, they could cut off a chunk from an armband or bracelet and weigh it, thus the name hacksilver. They literally wore their money!
Clearly, money is no simple, universal thing. Each nation and each time has its own coins with its own values. Your player characters may travel through many different lands and find long-lost treasures. It will be much more exciting for your characters to find 600 ancient tremissa from the rule of Emperor Otto 400 years before than to find yet another 600 silver pieces. With a little imagination and research at your local library, you can find many different examples to add to your campaign.