Epiphany Sunday originates from an ancient Christian holiday called the Feast of Epiphany. Christians celebrated this holiday on January 6 until the Roman Catholic Church changed the holiday to the first Sunday after the first Saturday in January.
References to the Feast of Epiphany date back to the writings of the Roman historian Ammianus Marcellinus in 361 A.D. Originally, all Christian churches celebrated January 6 as the day of Jesus' birth, but later the Western churches changed Christmas to December 25. Because the Eastern churches continued to celebrate the birth of Jesus on January 6, the Western churches mandated a twelve day feast from December 25 to January 6, also known as the Twelve Days of Christmas. In the 1960s the Roman Catholic Church and in the 1970s the Anglican Church declared that the Feast of Epiphany was to last eight days. Not all churches celebrate Epiphany Sunday, and Eastern and Western churches vary in the date upon which they celebrate Epiphany.
Epiphany Sunday celebrates the revelation of God in human form. This includes the visit of the three magi and the baptism of Jesus. Because the visit of the three magi carries the greatest weight during this celebration, Epiphany Sunday is also called Three Kings' Day.