Worshipers attend a Christmas Eve service according to the Eastern Orthodox calendar in the Church of the Nativity in the West Bank city of Bethlehem, Palestine, Jan. 6, 2016. Reuters

When talking religious festivals, it's often difficult to separate history and tradition. While the Bible does not actually reveal the month or even year that Jesus Christ was born, researchers have been able to put together a couple of narratives of the upcoming holiday and speculate just how Dec. 25 became Christmas for Catholics.

Christmas is often considered the second-most important Christian holiday after Easter, which celebrates the resurrection of Jesus, according to religious tradition. However, it wasn't always that way. While the modern calendar, known as the Gregorian Calendar and developed by Pope Gregory XIII in 1582, is actually based on the birth of Christ, Jesus' birth was not considered a major Church occasion for over 300 years. The abbreviations B.C. and A.D. still used today to measure history stand for "Before Christ" and anno Domini (Latin for "The year of our Lord"), respectively.

The first recorded observation of Christmas on Dec. 25th was discovered on a Roman calendar dating back to 336 A.D. Prior to this, the Church considered the Epiphany, celebrated on Jan. 6, to be the season's major holiday. This festival, also called Three Kings' Day, recognizes both the visit of three Magi kings to the infant Jesus after his birth in Nazareth, as well as the baptism of Jesus by the prophet John the Baptist in the Jordan River.

Who exactly made the decision to establish Christmas on Dec. 25 is still up for debate, as is the precise motivation. Historians, however, have found conclusive evidence that creates the prevailing narrative on the origins of the feast. Many believe the Catholic Church chose the date because it coincided with the winter solstice in the Julian Calendar, the predecessor to the Gregorian Calendar that is still followed by Eastern Orthodox denominations of Christianity. The solstice is the shortest day and longest night of the year and was revered by pagans as the birthday of the sun. The Church chose the date to compete with the heathens, according to 19th-century anthropologist James George Frazer.

Others disagree that the Church borrowed so heavily from pagan traditions. The Biblical Archaeological Society, a non-denominational organization dedicated to revealing the archaeological history of the Bible in the Middle East, highlighted the discussion of dating Jesus' birth among writers in Egypt, Syria and Palestine in the early days of the Church. In an article originally published in the organization's publication in 2002 and republished online Dec. 2, author Andrew McGowan of the Divinity School at Yale University highlighted the Judaic tradition of linking the births and deaths of prophets. Since Jesus' death was determined to have occurred around March 25, his death was placed exactly nine months later, the amount of time he would have spent in the womb of his mother, worshiped by Christians as the Blessed Mother and the Virgin Mary.

To be sure, not all Christians celebrate Christmas on Dec. 25. Because Eastern Orthodox denominations of Christianity still follow the Julius Calendar, nearly two weeks behind its Gregorian counterpart, Christmas is celebrated by Eastern Orthodox and Coptic Christians on Jan. 7. Armenians still celebrate Christmas on the date it was originally determined to have fallen on, Jan. 6, the same day as the Epiphany.