I researched something about this a couple of years ago and posted it on a board on which some guy was talking about it. This info comes from a book I have that was published in the 1940s. I realize that other interpretations of the Mayan calendar might vary, based on the opinion of the various researchers. Here is what I wrote a couple of years ago:

“I have a big chart in this book that shows the last time the Mayan calendar rolled over to 12-0-0-0-0, which was on September 20, 1618.

The time before that was 11-0-0-0-0 which was on June 17, 1224 AD.

The time before that was 10-0-0-0-0 which was March 15, 830 AD.

The time before that was 9-0-0-0-0, which occurred on December 11, 435 AD.

What will happen in the year 2012, when the Mayan calendar rolls over to 13-0-0-0-0 will merely be another roll-over in a Mayan 394 year cycle, and it will happen again in the year 2406, and this will keep on happening for millions of years. Nothing is going to be any more significant in the year 2012 – relative to the Mayan calendar – than was significant during the last roll-overs in the years 1618, 1224, 830, and 435 AD."