Origins of April Fools Day...
When the Church officially declared Dec. 25 to be the birthdate of Christ, in order to co opt a old pagen holiday (Festival of Myrna? I think) they decided the year should begin with his birth. So much like the timeline BC, AD, etc. the calander year begins on Jan. 1 to coincide with this idea.
The previous clander year was much like that still in use by China, etc. and begins with the seasonal return of life in the spring. Never mind Jesus was most likely ALSO born in the spring, politics and religious dogma are far more important than accuracy.
So AFTER the clander and timeline was recalibrated to the satisfaction of the Jesus folks, despite mathematical errors in the timeline itself, they recognized the start of the year as Jan. 1.
Many people resisted the NEW calander and continued to recognize the beginning of the NEW YEAR in the spring on the April 1 date. Thus anyone who did not accept the new mumbo jumbo was branded a "April Fool."