Lol, someone has Stargate on the brain.
Well, that's if they are, in fact, artifacts. I'm skeptical, especially of the Grail, because it only showed up for the first time in Perceval, le Conte du Graal. The author, Chrétien de Troyes, was - to use fantasy terms here - a bard, in the twelfth century. He was a creative mind, don't get me wrong, because he was what I would consider the father of true medieval literature, but that's just it: He was a bard. Bards tell stories. He got paid for writing stories his clients would like, and once the Arthurian legends got rolling, they were the rage. That's why there are so many stories that trickled down to us in modern times concerning them. The Grail itself really is only mentioned in these stories, 1100 years after Christ was supposedly crucified.
Of course, we still don't know 100% if Arthur was really a king or an archetype, so my skepticism may be proven wrong one day. And you really can't talk about the Grail without talking about Arthur and his knights, so...
As a side note, I'm not entirely sure I'd want Arthur himself to be proven to have existed, either. It's a great little mystery, and I'm afraid hard scientific fact of him would ruin the image I have of him in the stories. There was a book I read not long ago, by Bernard Cornwell, called The Winter King, which shoved Arthur into the historical record of the Dark Ages, but it presented him in such a way I felt the need to slap him silly. It's part of a series (that I have to finish, shame on me) that actually is pretty good. /tl;dr ot