With its soaring stone pyramids and geometric temples, Teotihuacan was once the biggest city in the Americas and possibly the world.
However, experts have never been able to say with certainty who built it and why it was suddenly abandoned.
An international team of experts believes the answer may lie under the Pyramid of the Sun, the centre point of the vast ruined city 25 miles outside Mexico City.
That should be interesting. Odd that nothing was removed from it when it was initially discovered which makes one wonder if there's nothing in there anyway.