Christmas, as a distinct Christian festival on December 25, first shows up in historical records in the 300s AD, with the earliest clear record from the year 336 in Rome. Over the next century or two, churches across the Roman Empire gradually adopted this celebration, and many older winter-solstice customs were absorbed into what became known as Christmas.

How Christmas Got Started

  • The earliest recorded celebration of Christmas is December 25, 336 AD, in a Roman almanac that notes “Christ born in Bethlehem, Judea.”
  • By the mid–4th century, church leaders in Rome were formally celebrating the birth of Jesus on December 25, and the date became part of the official church calendar.
  • Eastern Christian communities initially used other dates such as January 6, but over time many of them also adopted December 25 alongside their older traditions.

Why December 25?

  • The Bible does not give a specific date for Jesus’ birth, so early Christians had to choose one based on symbolism and theology rather than direct historical data.
  • One influential idea linked March 25 (seen by some early Christians as the date of Jesus’ conception) to a birth nine months later on December 25.
  • December 25 also overlapped with major Roman and Mediterranean solstice-time festivals such as Saturnalia and the feast of Sol Invictus, which may have helped Christians “reframe” an already popular season around Christ’s nativity.

Pagan Festivals and Christmas

  • In late antiquity, Romans celebrated Saturnalia and later the “birth of the Unconquered Sun” around the winter solstice with feasting, gift‑giving, and public revelry.
  • As Christianity became dominant in the empire, church leaders promoted a nativity festival that redirected this festive energy toward Jesus’ birth instead of the older pagan gods.
  • Some non-religious elements that people now associate with Christmas, such as greenery, yule customs, and general midwinter partying, trace back to these broader solstice traditions rather than to early Christian worship itself.

When “Christmas” Became the Modern Holiday

  • The English word “Christmas” (from “Christ’s mass”) appears in written sources by the 11th century, reflecting a firmly established church feast centered on a special Eucharistic service.
  • Medieval Europe added nativity plays, carols, and local customs, while later centuries brought Christmas trees, Santa‑style gift‑bringers, and a strong focus on family and home.
  • By the 19th century, especially in Britain and North America, Christmas evolved into the modern blend of religious observance and largely secular traditions that is familiar today.

TL;DR: Historically, Christmas “starts” as a formal, dated celebration in the mid‑4th century, with December 25 first clearly recorded as Jesus’ birthday feast in 336 AD, layered on top of older winter festivals and gradually expanded into the global holiday people recognize now.

Information gathered from public forums or data available on the internet and portrayed here.