In my long running game they found their first artifact at 5th a sword that slowly changed as it awakened +1, then frost, then +2 then frostbrand, and then a free counterspell against any fire spell within 60'. Somewhere along the way they realized it was the sword of a frost giant god, destined to bring an Ice age. They tried to stop it and would swear every time it increased in power.
At 13th lvl they obtained a second, the orb of lies. The only thing they got it to do at their command was to hide the first artifact. They thought they got it to do a lot of other things, but mostly it lied to them, it took amazingly long for them to stop trusting it.
The PCs got the sword off the prime, so it brought an ice age and a war to the outer planes instead.