Thanks for your answer.
However when they say it is "usually referenced" it doesn't really answer my question. What happened on that day that was written about using both calendars?
Well, I found this...
As Dr. Jose Arguelles writes in "Time and The Technosphere" -
"August 13, 3113 BC is as precise and accurate as one can get for a beginning of history: the first Egyptian dynasty is dated to ca 3100 BC; the first 'city,' Uruk, in Mesopotamia, also ca 3100 BC; the Hindu Kali Yuga, 3102 BC; and most interestingly, the division of time into 24 hours of 60 minutes each and each minute into 60 seconds [and the division of the circle into 360 degrees], also around 3100 BC, in Sumeria."
But that really doesn't provide a good reasoning for syncing the Mayan calendar with that date.
The Book Of Knowledge has this to say:
According to the correlation between the Long Count and Western calendars accepted by the great majority of Maya researchers (known as the Goodman-Martinez-Thompson, or GMT, correlation), this starting-point is equivalent to August 11, 3114 BCE in the proleptic Gregorian calendar or 6 September in the Julian calendar (−3113 astronomical). The GMT correlation was chosen by John Eric Sydney Thompson in 1935 on the basis of earlier correlations by Joseph Goodman in 1905 (August 11), Juan Martínez Hernández in 1926 (August 12), and Thompson himself in 1927 (August 13).
Following one of the references from that article, (specifically, #8) we find this:
the zenithal passage of the sun over Copán -- the major Maya astronomical center in the mountains of western Honduras, located at precisely the same latitude as Izapa -- occurred on August 13, the day that his own correlation originally indicated the Maya had believed was the "beginning of the world,"
We get a good reasoning for the date, if not the year.
The year correlation was apparently done via computer analysis, as found later in that same article...
Sure enough, the only other time that a katun had ended on 8 Cumku was on September 13, 1675 B.C., when 1 Ahau corresponded with that date. I therefore was led to conclude that whoever had projected the time-count back into history had done so in the year 236 B.C., because this was the only time frame that would have been consistent with what we know of Maya history.
So there you go. The Mayans told us the date, by telling us the date (in long count) that it was enacted.
