The Arch-Magus Jovis was accredited with creating the first Disque Esprit, or spirit disc. During the early years of the Old Empire, the land was all but bursting with fallen shades and corrupted spirits that some would name demons. The organization of the Imperial Legions, the building of stone roads, and the proliferation of relics such as the Disque Esprit consolidated the power of the empire.
Each disc is similar in basic shape and construction. The key point is a stone torus, or donut. It is a minimum of 18 inches wide, or the span of two hands outstretched. It is also three inches thick and made of a single piece of hand carved stone. Most of the surviving discs are durable granite, basalt, and other hard stones. Records from the empire relate the discs were also made of serpentine, silver, gold, and other semi-precious stones. Few, if any, of these have survived to the current day.
The disc is suspended by a rope from a stone crossmember made of the same material as the torus. Most houses and buildings dating back to the old empire have an alcove, or hearth with odd stone fittings for the placement of the Disque Esprit. In the latter days, the artistic value, as well as material value of a disc was as important as the spirit protection it provided.
A Disque Esprit creates an area that is effectively off-limits to spirits, IE - ghosts, elementals, demons, and other incorporeal outsiders. Some even generated an effect that warded a building against corporeal spirits such as materialized demons, elementals and physical undead such as zombies and vampires. Some rumor that the Disque is the source of the legend that a vampire must be invited into a house before he may enter.
A spirit cannot physically touch a disc. Doing so, or having the disc touched to them threatens to destroy said spirit, unless it is able to resist the power of the disc. Some discs, generally the smaller ones, are weaker as are ones that are made of less valuable materials.
Following the end of the Old Empire, the ranks of spirits, long bent to the laws and wills of the imperials retaliated as best they could. Many cities remained secure as their disques repelled spirits. Others were undone as the fell spirits corrupted wanderers and vagrants, enticing them to destroy and despoil discs, and leading to the ruination of many outlying communities.
Fetch - A city noble, or castellian has managed, to his great embarassment, loose his families Disque. The loss has remained secret, but the Castellian is willing to do most anything to see that it is returned, and to make sure no one knows it was ever lost. As a corollary, the Castellian, after the disque is returned from the thieves den/monsters lair/wherever, decides to have the PCs executed, or otherwise murdered.
Desperate Gambit - The PCs are approached by the lord of a desperate land, overrun with demons and monsters. He beseeches the PCs to find, and return with a Disque. The rewards are impressive, but the potential to make enemies is equally impressive.