The pre-Columbian cultures of Mesoamerica practiced a form of geomancy in which elements of the natural environment attained supernatural significance and were used to structure the cultural landscape. Thus caves, springs, mountains, and other natural formations were transformed into "cosmo-magical symbols" (Wheatley 1971) relating to mytho-religious beliefs. Tlachihualtepetl or "man-made mountain" as the Great Pyramid was known at the time of the Spanish Conquest, is by volume the largest construction from pre-Columbian Mesoamerica (Marquina 1970a; McCafferty 1996a). It is also the oldest continuously used ceremonial structure in the Americas, and as such can be viewed as a palimpsest of iconographic information accumulated during a period of 2,500 years. The Great Pyramid is located over a spring, which flows from beneath the mound east into the former lake. Thus the Pyramid embodies the concept of altepetl, literally a water-mountain that for later Nahuas was the metaphoric term for "kingdom".