Artifacts are extremely powerful. Rather than merely another form of magical equipment, they are the sorts of legendary relics that whole campaigns can be based on. Each could be the center of a whole set of adventures—a quest to recover it, a fight against an opponent wielding it, a mission to cause its destruction, and so on.
Unlike normal magic items, artifacts are not easily destroyed. Instead of construction information, each artifact includes one possible means by which it might be destroyed.
Artifacts can never be purchased, nor are they found as part of a random treasure hoard. When placing an artifact in your game, be sure to consider its impact and role. Remember that artifacts are fickle objects, and if they become too much of a nuisance, they can easily disappear or become lost once again.
Source: The Book of Divine Magic
Relics – sometimes also called reliquaries – are sacred magic items. Relics are objects (or they contain objects) that were somehow connected to a saint or other important religious figure. Sometimes the reliquary is an object – such as a sword, staff, or amulet – that was used by the saint. Other times, the relic contains or is made of pieces of clothing the saint wore, pieces of a chair the saint sat in, pieces of a burial shroud the saint was covered with, and sometimes even the bones, hair or teeth of the saint herself. On rare occasions, a relic is a piece of artwork – called an icon – that depicts the saint.
Editor’s Note: More information on relics and their creation please see Relics.
Minor artifacts are not necessarily unique items. Even so, they are magic items that no longer can be created, at least by common mortal means.
Major artifacts are unique items—only one of each such item exists. These are the most potent of magic items, capable of altering the balance of a campaign. Unlike all other magic items, major artifacts are not easily destroyed. Each should have only a single, specific means of destruction.
Reliquaries are in many ways similar to artifacts. They are unique and one cannot create a duplicate short of using a carefully worded wish spell (even then, odds are very, very low that the duplicate would actually function in the same manner as the original). Unlike artifacts, or other magic items, relics are not created. Relics gain their divine power either through the will of the saint they were part of or belonged to, through the will of the faithful who direct prayers toward the relic, or through the direct divine intervention of the deity the relic is sacred to. Reliquaries are never found in random treasure hoards and are never offered for sale by anyone but the most unscrupulous of fences. Most reliquaries are in the possession of a priest or temple and are jealously guarded at all times.