You can capture maximum of 3 artefacts out of which only 1 can be unique or account wide. To have more than 3 artefacts in your account. The artefacts must be conquered by conquering the whole village that holds them.
Only the 3 oldest artefacts are active out of which only 1 can be unique or have an account wide effect. In case there are 2 account wide effect artefacts amongst your 3 oldest artefacts the fourth oldest will become active.