What's the Origin of April Fools' Day?

What's the Origin
of April Fools' Day?.
The April 1 tradition of pranks has been observed
for several centuries across a variety of cultures.
However, the official origins of
April Fools’ Day are unknown.
The most popular theory is that the day was
caused by the switch from the Julian calendar
to the Gregorian calendar in the 16th century.
The original calendar saw the New Year
beginning on March 25, with celebrations
occurring on the first day of April.
The switch moved the New Year to January 1,
but many still thought April 1 was the proper day
to celebrate, hence they were “April fools.”.
Another theory says the day is related
to the arrival of Spring, when nature
“fools” people with irregular weather.
Historians have also linked April Fools' Day to an
ancient Roman festival known as Hilaria, which
was celebrated by people dressing up in disguises.
Whatever its origin may be, April Fools’ Day
has evolved to have its own lore and rules.
Superstition says that playing pranks
past noon or not responding to pranks
with good humor will attract bad luck