When the Louisiana Superdome opened in 1975, its brochure compared it with other "stadia".
We are using Latin words that are now part of the English language - we are not speaking Latin here (except in my signature). I think that they should have used "stadiums" rather than "stadia" in this case.
In medical or legal usage, maybe. But this came off as being pretentious, IMO.
Me transmitte sursum, Caledoni!