In 2010, a robotic explorer was sent to explore a recently discovered tunnel under the famous site of Teotihuacan outside of Mexico City. What the robot saw was a tunnel, with an arched roof, with stone-working technology and skill clearly in evidence. Archaeologists were hoping to find a tomb at the end of the tunnel, which would provide more clues as to the nature of the civilization that built the magnificent site, for when the Aztecs arrived in the Valley of Mexico ca 1300, they discovered the site already vacated. The mystery of the site has always been that, unlike the Mayan ruins much further south, no sculptures or images of any of the civilization's kings were ever discovered at Teotihuacan.
Compounding the mystery is that Teotihuacan contains at least 1200 burial sites, including the tomb of a man discovered in 1998. The man had been bound and apparently sacrificed, with the tomb itself full of various precious and valuable objects. Additionally, while conventional archaeology originally thought the Toltecs to have built the site, it became evident that the word "Toltec" simply meant highly skilled craftsmen, which the builders of the site, whoever they may have been, were. The presence of human and animal sacrifice at the site is palpable, and Wikipedia states that among the preferred "methods" of this barbaric practice, were beheadings, removal of the heart, or simply being buried alive, presumably as dedications of new buildings.
This barbaric practice seems to have arisen because of the common belief that everything sprang into existence because of the gods' having literally dismembered - sacrificed - themselves to bring everything into existence. Sacrifice was thus not only a debt to be repaid, as co-author Scott D. deHart and I noted in The Grid of the Gods, but also was a deep topological metaphor of the physical medium and its differentiations. As we noted there, the practice appears to have originated from India, which, oddly, subsequently more or less abandoned it, at least in ritual terms that would parallel Mesoamerican practice.
This fact, however, points to a possible origin of whoever built Teotihuacan, for as we also pointed out in Grid of the Gods, the most recent findings of genetics and archaeology - if one keeps an open mind rather than following the "Siberian-Alaskan Land Bridge" dogma - is that the Americas may have been settled long ago by pilgrims arriving across the Pacific, and ultimately from India. But of course, that's archaeological heresy, which even to entertain, brands one with the usual ad hominems. But in my opinion, it nevertheless remains true, that the mystery of Teotihuacan cannot be solved simply by looking at Mesoamerican antecedents and descendents...it is part of a much wider, global mystery.