SOLVED. Sci-Fi. Sufficiently advanced civilization creates a world with Norse Gods and civilization for them to fight. [s]

[Trey]

Folks, can you help me out here? I’m trying to remember a novel from either the 80’s or 90’s where a sufficiently advanced civilization creates a world with the Norse gods and a medieval society for them to fight, all for the civilization’s entertainment. However, the creators screw up and both sides figure out what’s up. And then decide that they'd rather fight their creators.
But I can’t recall the title.
Anyone able to help me out?

[Ayshe]

Project Millennium maybe?

[Trey]

I think that's it!
Thank you!