Basement, then crawl space, then first floor - why 2 layers?

[Tim P.]

I am looking at an old house that strangely has an unfinished basement, then a crawl space above it with joists/subfloor, and then the first floor's joists/subfloor above that.  2 layers of unfinished space below the first floor.  Has anyone ever seen this before, and what is the purpose?  Most of the plumbing is located in the crawl space section, not the basement.

(P.S. sorry if this is the wrong forum, I couldn't find a "construction" or "home inspection" forum.)