There's a lot we can tell about an ancient building through archaeology and scientific research. We can tell when it was built, and usually how it was built, too. We might even be able to get an idea of what it was used for, but we can't always get all of the answers. Every structure you're about to see in this list is an outstanding feat of ancient construction, and although we know a little about all of them, we're still left with more questions than answers.