If there is one piece of proof of the coming 2012 catastrolypse that the Conspiracy has been unable to suppress, it is the well-known end to the Mayan calendar. Or, technically, the end of one of their calendars. Whatever. But this isn't like some issue where they just needed to upgrade to "Mayan Outlook 2007" and get a date fix - their calendar comes to a screeching halt for a reason. Or it resets. Whatever.
The Maya, as you may or may not care, was an advanced Mesoamerican civilization that traces its organized roots back to approximately 1800 BC. The civilization flourished from AD 250 until AD 900, with a vibrant culture, sophisticated architecture and technology, and exceptional achievements in language and the sciences. The Maya civilization mysteriously collapsed sometime around AD 900-1000 - one of the greatest mysteries in modern archaeology. Contrary to common belief, the collapse of the Maya had nothing to do with Spanish Conquistadors, Aztecs or various common intestinal illnesses.
The Maya (or "Mayans") were unquestionably highly sophisticated in their understanding of astronomy and its relation to seasonal cycles. The Maya used a number of different cyclical calendars, including the 260-day Tzolk'in and the 365-day Haab' which were used together to provide relative dates; while their historical dates were recorded using a system commonly called the Long Count. (Interestingly, the Long Count calendar is one of the first recorded uses of the mathematical concept of a "zero" or placeholder number - an innovation Western cultures did not adopt for many years.) Other Maya calendars in sometime use included those with intervals of 9, 13 or 819 days. History does not record if there was a Maya equivalent to the Hallmark Corporation but if there was, they clearly made a killing.
The Maya concept of the world was cyclical in nature: cycles of death and rebirth. The combination of the Tzolk'in and Haab coincided every 52 years - at the time, significantly longer than the average person's lifespan - and this rare occurrence was seen as a time of bad luck. Like some other mesoamerican cultures, the Maya believed that their existence was tenuous and subject to continued approval from (and sacrifice to) their gods who might at any time end their world and start anew. The Long Calendar dates "roll over" every 144,000 days.
Enough with boring history and math - let's get to where ancient books of prophecy come in.
According to one post-decline Mayan mythology book called the Popol Vuh, the gods had run through a number of these cycles, each time reinventing the world but ultimately finding their creation unsatisfactory and starting again. The fourth of these great cycles (the Fourth World, the age of humans) began at a certain point in the Long Count calendar. The next time the calendar cycles through - and hence ripe for a new cycle to begin is - wait for it - DECEMBER 21, 2012. This is the time for the Fifth Age to begin - whether through the destruction of the Fourth World or its transformation into something else is unknown. Frankly, if we were the gods, we would look at this Fourth Age of Men and after watching only an hour or two of basic cable television, we would pretty quickly conclude things had gone terribly wrong and it was time for starting over, too.
Now, for most reasonable people, the fact that a book of mythology from a vanished ancient culture predicted a new historical cycle would be enough to convince them of impending doom. However, when you add to that the overwhelming weight of similar ancient predictions, the undeniable link to the 26,000-year precession of equinoxes and proliferating modern signs of impending catastrolypse, the evidence becomes so overwhelming that it is so true that it goes off the scale of trueness to something entirely new like ... HYERULTRATRUENESS TO THE INFINITY POWER. Even the ninja-like-megatrueness of the 2012 catastrolypse.
Unfortunately, the Conspiracy is busy at work trying to keep people from understanding the supergigatrueness. "Scientists" make pathetic claims like "We have no record or knowledge that [the Maya] would think the world would come to an end" or that the 12/21/2012 prophecy is "a complete fabrication and a chance for a lot of people to cash in."
Fortunately, those of us in the Know are immune to the lies of the Conspiracy and can do what is necessary to begin panicking early and often.