The earliest recorded association between April 1 and practical jokes and
all sorts foolishness can be found in Chaucer’s Canterbury Tales (1392).  

Saint Valentine’s Day, commonly called Valentine’s Day, began as a holiday
observed on February 14 honoring one or more early Christian martyrs named
Saint Valentine. It was first established by Pope Gelasius in 496 AD, and was later deleted from the General Roman Calendar of saints in 1969 by Pope Paul VI. 

1953