When I try to place the last artifact in the 3rd temple the guy doesn't
show up to talk to me.Any ideas?

Well, that's very strange. If you placed the other two doodads, then you have to be in the right place with the right one for this temple. Is that the ruined temple? Remember you have to walk through the center for Altheides to show up. That stuff in the center isn't harmful, so just walk straight through it.

This is all I can come up with; no one's ever had this problem before.

<center>Nightowl2</center>