There are three different categories of artefacts available; village, account and unique. Village artefacts only affect the village they are stored in, account artefacts effect the whole account and unique artefacts do the same but with a greater bonus.  

At any one time each player is only allowed to use a maximum of three artefacts, of which only one can be of the account or unique type. Players may however hold more than 3 artefacts but only the 3 oldest artefacts will be used. To hold more than 3 artefacts, additional artefacts must be captured by chiefing the village in which the desired new artefact is located. To capture a second unique or account level artefact, this chiefing method must be used, as the standard limit is one unique/account and two village artefacts per account. Furthermore any village artefacts will overwrite the bonus of account or unique artefacts of the same type for the village they are in effect for.

Artefacts will spawn in Natarian villages and will be inactive there until they are captured. In order to capture an artefact you need a treasury of level 10 for a village artefact or level 20 for an account or unique artefact. The treasury holding the artefact must be destroyed and a successful normal attack with a hero sent from the village containing your treasury in order to capture the artefact. Artefacts will not activate until 24 hours after they have been captured (this includes capturing artefacts that you already owned).

HINT: After one month of the artefacts being added to a server, any artefact that is still in a Natarian village will become active with the associated benefits being applied to that Natarian village / account as appropriate.