I present to you "Trench War" by concept artist Tim Tao! I don't think I've seen those before. In fact, I think leaks of this edition use to be pre-alpha screenshots and 3D models rather than concept art, which should make this pretty rare content. They're labelled as being made for Blizzard North in 2004. As points of reference, this would place them in the year after Diablo 2 Patch 1.10 and the year before Blizzard North's closure in 2005. I can imagine how these scenes may have evolved into Azmodan's battlefields in Act 3.
Hmm, I found some more here from the same artist, although this time no longer concept art.
It's from the same timeframe in 2004, and actually much of it might be for the same scenes the concept above was created for, only a little further developed into 3D. Seeing a lot of similar, wooden trench like structures here.
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