Established under the reign of Horatus III the Wizard King, the mages guild regulates the use of magic throughout the Empire under the authority of the emperor. They ensure that magical artefacts are properly used and in the right hands, that rituals are only sold where appropriate and endeavour to prevent wizards from using magic to exploit others. Although their original charter was that of 'magical law enforcement', the mages guild has since evolved into more of a corporate entity.
The guild is currently responsible for the sale and production of residium, the key component in rituals, which has made them extremely rich. They dedicate these funds to magical research and development, as well as accumulating powerful magical items and tomes. The head of the guild, the Lord Mage, commands the province of Mageshire, telling of the guilds wealth and power. Those who try to circumvent the guild's taxes or regulations often find themselves on the wrong end of a guild auditors fireball spell.
Residium is a highly valuable spell component required in the casting of rituals. As it is essential for mages, it is extremely expensive, and the guild makes a fortune out of monopolising its supply. Those who break their license to supply are subject to the whims of the auditors, however competition is rare due to the difficulty inherent in manufacturing residium.
To create the fine white magical dust, one must refine a magical concentrate known as soulgems. These soulgems are created when a living entity dies, and the more powerful the being the more potent the gem. These gems are crushed and put into arcane machines called refineries to produce the final product. (just a question, is this like something dies, and then a gem pops out from the ground or something? Or is there a magical process behind collecting these gems?)
Since deposits of naturally occurring soulgems are rare the guild keeps their locations secret. If the mines and refineries were found and taken by a third party, it would earn the new owner hundreds of thousands if not millions of gold pieces.
The auditors are the enforcers of the mages guild. They ensure that magicans not paying guild rates, performing forbidden magic or selling illegal magewares are arrested. Though the auditors are mainly glorified battlemages, some of their number are legitimate detectives. Usually they are not involved in persecuting minor infringements, instead saving their resources for major concerns, such as taking down dangerous portals or fighting the Arcane Cartel.
The guild keeps many of its most valuable and dangerous secrets 'off world'. It is well known that the guild possesses its own personal demi-plane known as the spellvault for conducting magical research, keep dangerous criminals captive and storing residium called the spellvault. However, the secret of how to enter the spellvault is a well kept one, and is sought after by many mages. It is believed that only the chosen 'keepers' or higher ups within the guild may access the plane. Considering the spellvault supposedly holds realms of forgotten magic tomes and items all mages dream of having access to such a place. Some of the guilds enemies are dedicated to finding the entrances so they may plunder freely and possibly destroy the guild with its darker secrets.
Within the city of Tallowkeep stands a mammoth building which claims to hold a copy of nearly every book ever written. It is hard to doubt this claim, especially when one sees the rows upon rows of books stacked to the ceiling. The cost of admission to the chamber is one book, and the cost of borrowing is the donation of a unique tome. The most valuable books in the collection are kept in individual heavily guarded chambers beneath the library proper. Supposedly, no one has ever read every book within the library.
Another essential service of the mages guild is it teleportation network. With travel from one side of the empire taking up to months, the opportunity for faster travel is greatly appreciated. The guild can provide instant travel from point to point across the Empire, for a fee of course. Despite being quite high, at a thousand gold pieces per person or one hundred kilograms, and only available when residium stocks are high enough, there is still strong demand. While the portal does offer benefits to merchants and fast travelers, it also poses the threat that if one portal and its pass code were captured, an army could teleport into the middle of any major settlement.