Christmas is an annual festival commemorating the birth of Jesus Christ, observed primarily on December 25[a] as a religious and cultural celebration among billions of people around the world. It is a feast central to Christianity. In the liturgical year, preparation for Christmas begins on the First Sunday of Advent (the fourth Sunday before), and it is followed by Christmastide, which historically in the West lasts twelve days and culminates on Twelfth Night. Christmas Day is a public holiday in many countries, is celebrated religiously by a majority of Christians, as well as culturally by many non-Christians, and forms an integral part of the holiday season surrounding it. The traditional Christmas narrative recounted in the New Testament, known as the Nativity of Jesus, says that Jesus was born in Bethlehem, in accordance with messianic prophecies. When Joseph and Mary arrived in the city, the inn had no room, and so they were offered a stable where the Christ Child was soon born, with angels proclaiming this news to shepherds, who then spread the word. There are different hypotheses regarding the date of Jesus's birth. In the early fourth century, the church fixed the date as December 25, the date of the winter solstice in the Roman calendar. It is nine months after Annunciation on March 25, also the Roman date of the spring equinox. Most Christians celebrate on December 25 in the Gregorian calendar, which has been adopted almost universally in the civil calendars used in countries throughout the world. However, part of the Eastern Christian Churches celebrate Christmas on December 25 of the older Julian calendar, which currently corresponds to January 7 in the Gregorian calendar. For Christians, believing that God came into the world in the form of man to atone for the sins of humanity rather than knowing Jesus's exact birth date is considered to be the primary purpose of celebrating Christmas. The customs associated with Christmas in various countries have a mix of pre-Christian, Christian, and secular themes and origins. Popular holiday traditions include gift giving; completing an Advent calendar or Advent wreath; Christmas music and caroling; watching Christmas movies; viewing a Nativity play; an exchange of Christmas cards; attending church services; a special meal; and displaying various Christmas decorations, including Christmas trees, Christmas lights, nativity scenes, garlands, wreaths, mistletoe, and holly. Additionally, several related and often interchangeable figures, known as Santa Claus, Father Christmas, Saint Nicholas, and Christkind, are associated with bringing gifts to children during the Christmas season and have their own body of traditions and lore. Because gift-giving and many other aspects of the Christmas festival involve heightened economic activity, the holiday has become a significant event and a key sales period for retailers and businesses. Over the past few centuries, Christmas has had a steadily growing economic effect in many regions of the world.