To put that in context, the Hindu-Arabic numeral system, which we now use, and most of the world now uses, it wasn't devised, we don't believe, until about a thousand years later. And it wasn't adopted in Europe until about 2000 years after the time where we see the first evidence of this Mayan numeral system, this base 20 system, that had place value. Now, around the third century BCE, so roughly in this time period right over here, we see the first writing. And these are examples of what a Mayan glyph looks like. So that is a Mayan glyph, and you read it in an order like this. And once again, this is a very early form of writing, and it's believed to be the first form of writing, well-established writing, in the Americas. Now, on top of their sophisticated numeral system and the writing that they developed, they also had a very sophisticated calendar.