The custom of playing practical jokes on friends was part
of the celebrations in ancient Rome on March 25 (Hilaria) and in India on March 31 (Huli).
The timing seems related to the vernal equinox and the
coming of spring-a time when nature fools us with sudden changes between showers and sunshine.
April Fool's Day is thought to have originated in France.
Before the use of the Gregorian calendar, New Year's celebrations
ended on April 1st.
When New Year's Day was changed to January 1st,
the people who still celebrated it on April 1st were called April Fools.