Walking through Teotihuacan is an impressive experience, but one can only imagine what it was like over a thousand years ago. The sheer magnitude of the pyramids is awesome, but the use of mathematics and astronomy in the planning is also quite fascinating. Many people associate the pyramids with the Aztecs, but they were actually built before the arrival of the Aztecs and abandoned by their creators. How could you leave something so magnificent? Then again, every empire eventually crumbles.