DEUS EX MACHINA
In modern terms, the "deus ex machina" describes a being, object or event that suddenly appears and solves a seemingly insoluble difficulty. Such would seem to be the case with this contraption, as I'm not really sure what it does. I suspect it's demonstrating how the stones were lifted into place, but I couldn't find a plaque anywhere to shed light on its function. One of those ancient mysteries, I guess.