Trading is the exchange of one or more goods for a different good or goods of equal value between two parties or individuals. The direct exchange of goods is called bartering, while the exchange of a good for a certain amount of coins is more commonly reffered to as trading.
Domestic trade is trade between members of the same country.
The largest settlements, the Six Cities, could be argued as representing a different Avernite industry. In Northeastern Exile, Formello with its proximity to the Dragon Motrax in the old days and its library maintains a healthy profit from magic. Meanwhile, Silvar due its location between the Tower Colony and Fort Avernum, the two portal systems of Avernum, is a key trading hub. West of Silvar lies Cotra, a lakeside city that makes a profit off of fishing. South of the Eastern Gallery where these two cities lie is Almaria, which is famous for its wine industry. Blosk, on the other end of the Great Cave is primarily an agricultural venture, growing mushrooms. Lastly, Dharmon near Blosk is in the very profitable business of mining.
In Avernum, there is often banditry of all types on the roads, and the kingdom is usually always in some sort of problem. For example, in the days of the First Slith War, bandits, Nephil, and Slithzerikai all roamed the Eastern Gallery, waylaying Avernites. And no sooner had this problem been cleared by Hawthorne's Assassins, than the Empire-Avernum War began and the trade routes became very strained. What's more, the Time of Shades was arguably the worst time for trade, as entire cities would shut down in fear of destruction. As such, during these times, it was only safe to send out adventurers to deliver goods for pay, and the Avernites became phobic of large trade caravans.
However, in times of peace, trade flourishes much more. Merchants and their guards travel the caves, trading goods between cities. Also key to trade is the rivers and lakes, where barges ladden with goods can travel safely at most times and deliver goods from places like the Great Cave directly to remote places like Fort Monastery. Lately, King Starrus set up a new feature for Fort Avernum, that of pylons. These pylons are set up in most settlements of Avernum, and upon traveling to Fort Avernum, one can use them to go to any of the pylons one has visited, and back. This is a revolutionary new idea that will essentially make Fort Avernum a trade hub once the project is released to the public.
In the vast Empire of the Surface, things are much different than in Avernum. Since the Empire has spanned across all four continents, it has a wide variety of goods. Thus, the economy focuses centrally on transporting goods from one place to another.
The Imperial Army has long since ended banditry in its settled parts, and minor pests like Goblins are quickly and lethally dealt with by adventurers or guards. As such, large caravans of merchants, like travelling cities, wander from city to city, usually staying in a single continent, and trade. These caravans often work in a massive circuit, bringing food from one area to another, collecting ores there to bring to a different place, etc. These caravans often have horses to improve travel time, and are protected by mercenaries. This type of intracontinental trade is very profitable, and is quite important to the economy of the Empire.
The Sailor's Association, kept in check by the Imperial Navy is absolutely pivotal to the Imperial economy. The sailors have large seaworthy ships that go between all of the continents of the Surface. Most of these ships travel back and forth between Pralgad and the other continents, delivering ores and foodstuffs from Valorim, spices and gemstones from Vantanas, and textiles and lumber from Aizo. From here, Pralgadians manufacture the raw materials into various goods and ship them back to the other continents for use.
The Surface Portal
The Surface Portal in the Tower Colony of Avernum is the primary source of international trade. From here, the portal takes goods from Avernum to major trade centers across the Empire, and Upper Avernum. These goods, most commonly ores and crystals are then exchanged for Surface goods, ranging from Surface food to magical tomes. Then, the traders return through the Surface Portal and trade the goods with the Avernites. Thus the cycle of trade between nations continues. To capitalize directly on this type of trade, both governments require a fee to be paid to use the portal. This fee also helps maintain the portals, which can be very costly.
The other way international trade happens is directly through the Surface. As Avernum has two provinces on the Surface, Upper Avernum and Provincial Avernum, there is the possibility for direct trade between the nations here. Goods from all over Valorim are brought to Krizsan Province and Karnold Province, where they are exchanged with Fort Emergence and the City of Dawn respectively. Here they are bought by the Avernites, and goods like ores, mushrooms, magical research, are sold back to the Imperial citizens. Like use of the Surface Portal, going back and forth between the Empire and Provincial Avernum or Upper Avernum has a fee.
Some time after the Time of Shades, the Empire established three diplomatic outposts, one in the Great Cave, one in the Eastern Gallery, and one near the Northern Frontier. These were essentially the Empire's embassies to Avernum in Exile, just as Provincial Avernum was essentially the embassy to the Empire. In order to foster positive relations with the Avernites, as well as the sheer expense of the project, Empress Prazac I encouraged building material to be purchased from the Avernites. The portals linking the three settlements with the Surface are also of importance to trade between the nations, with goods from the Surface being brought down cheaper than through the Surface Portal. Most is used by the Imperial Army, but surplus sometimes finds its way into the hands of the Avernites.