Since they made no adjustment to allow for the difference (as we do by adding an extra day every leap year), this meant that New Year's Day of the civil year shifted slowly around the natural year.
For while you are breathing from January to January, the natural year is breathing by a different schedule.
The Egyptians are credited with the discovery of the natural year, and it formed the basis of the later Julian and Gregorian calendars.
Thus, the Babylonian calendar until the end preserved a vestige of the original bipartition of the natural year into two seasons.
The natural year was actually 365.25 days long instead of 365.
Differing pagan groups emphasise different events but the common themes relate to the cycle of the natural year and old agricultural related themes such as spring planting and autumn harvest.
The Gregorian calendar uses a simplified convention which has the effect of greater variance with the natural year.
Now, because the natural year is approximately 365 days and 6 hours, it means that approximately every four years we have an extra day in the year - hence the leap years.