"For there are no fixed natural limits of day, but if morning and evening, or still more clearly sunrise and sunset, are chosen as the limits, these must change every day and the days will vary in lenght.

 

Here the midnight period proved of assistance, since it facilitated the establishing of a fixed point of divergence. This was done in Rome, and the practice had its root in daily life, where in order to indicate the time of occurence of events, which took place in the night-time the calculation was pushed forwards on both sides towards midnight, until this became the limit of divergence. It is however an artificial epoch that must be found by calculation."

 

"Winter and summer, like all natural seasons, had at first no fixed limits. The quarters arose in the course of the reckoning, the people counting forwards in the first half of the half-year and backwards in the other half. The middle points of mid-winter and midsummer, fell where both reckonings met. This agrees with the popular objection to high numbers."

 

(Nilsson)

 

Now this also might explain why the sun is just a mirror image of himself after noon. Also it reminds me of a myth about the ten sons of Sina.