It's the tallest known pyramid in the New World and possibly the biggest pyramid by volume on earth, 2.8 million cubic meters.
For years, it was mistaken for a big hill.
Amazingly, this pyramid was unknown just a few decades ago and is part of collection of ruins covering an area bigger than downtown Los Angeles.
Stories like this are a reminder to take schoolbook archeology with a grain of salt. Not only do we not know all that there is to know, it appears that people trying to get the answers aren't getting much help figuring it out.