One of the high points of the Christian calendar is undoubtedly our celebration of Easter. The resurrection of Jesus following his death for us is at the very core of our faith.
For the earliest Christians the Christian year centered on the Paschal (Easter) feast, a great commemoration of the the death and resurrection of Jesus. Saint Ambrose of Milan referred to the three days starting with Good Friday as the the three most sacred days of Christian time. This early emphasis on celebrating Christ’s resurrection stands in contrast with the relative lack of recognition of any kind of holiday for His birth. Christmas became more important in later years.
There was some controversy among the early believers on when Jesus’ resurrection should be celebrated. Finally, in 325 A.D. Emperor Constantine met with other church leaders and they decided that Easter would fall on the first Sunday after the first full moon after the spring equinox. Most Christians have followed that calendar ever since.
Of course, Easter celebrations have not focused on Jesus alone for many centuries. As Christianity spread to numerous peoples and cultures around the world, various pagan groups added in their own springtime and fertility observances. Thus we now have Easter Bunnies and Easter Eggs to add to (or detract from?) this most meaningful of Christian holy days.
One web site I discovered with much more information on this topic is at
http://www.allaboutjesuschrist.org/history-of-easter-faq.htm
Happy Easter!