Another fascinating feature of some of the pyramidal structures (of Teotihuacan) is that they contain a broad, thick layer of mica, which had to be brought from Brazil, over 2000 miles away! If you know anything about mica, it's very flaky and fragile, yet it was brought in very large pieces from great distances (and without wheeled vehicles). Then the mica was used on an inner layer of the pyramid, not where it could be seen. Why?