That's right, it simply means "cannot read and write" - but that's my point .. even in spite of the fact that the end assembly process was being done by folks who could not read/write (most of the time) they were still able to assemble these extraordinary structures using the technology available to them.

And the technology of communicating to these craftsmen and artisans is another subject itself .. here in Vienna, we also have museums devoted to such things. I find it really fascinating personally.