Artifacts are special items with unique names that can be obtained by using the Stealing skill to pilfer them from various environments, through specific monster drop systems, from drops during events associated with game-wide fiction, or by crafting them using rare ingredients.

The original Artifacts were introduced in the Age of Shadows expansion in the dungeon Doom. Various items spawned throughout the dungeon that could only be picked up by using the Stealing skill on them. This was a move by the development team to vindicate the concept of collecting Rares, and as a throwback to the way that Rares had originally been created - as items, unobtainable to players, that had been used to decorate the environment, but had been accidentally left unlocked and could be picked up and wandered off with. These stealable items were spawned with a new item property called Artifact Rarity, which denoted the frequency with which they spawned.

Artifacts that adhere to the policy of possessing the Rarity item property can be classified into several categories.

* Doom Artifacts - Artifacts that can be found in Doom. These fall into two categories:
o Items that can be stolen in Doom.
o Items that drop in the Gauntlet.
# Virtue Artifacts - Artifacts that have begun spawning in the eight original Anti-Virtue Dungeons.
# Other Artifacts - There are also several other artifacts, such as The Redeemer, which could be acquired through quests, in-game events, or by other means.

Other Artifacts

It is also common parlance to call several other types of items Artifacts, even though they do not possess the Artifact Rarity property.

* Ilshenar Minor Artifacts - Items that drop as part of the Paragon system in Ilshenar, several of which are exclusive to this system.
* Treasure Map Minor Artifacts - Items that drop from Treasure Maps. These items include those that drop as part of the Paragon system, as well as some which are exclusive to Treasure Maps.
* Leviathan Minor Artifacts - Items that drop from the Leviathan, a sea monster that is spawned through use of a certain fishing net. These items include those that drop as part of the Paragon system, as well as some which are exlusive to the Leviathan.
# Mondain's Legacy Minor Artifacts - Items that drop in the same style as those associated with the Paragon system, but only in Mondain's Legacy Dungeons or from Peerless bosses.
# Peerless Artifacts - Items that spawn only on the corpses of Peerless bosses. Each Peerless boss spawns specific artifacts.
# Craftable Artifacts - Craftable items that, due to their high end properties, are considered artifacts. Rare ingredients available only from Peerless monsters are required to craft them.
# Champion Spawn Artifacts - Artifacts that can be obtained when killing a Champion.

For a complete list of artifacts and their properties (Not exact, but fairly close documentation):
http://www.uoguide.com/Artifacts