There is no certainty on when the Advent season came to be, however it was certainly in existence from about 480 with the introduction of a novelty that ordered monks to fast every day in December until Christmas. According to Saint Gregory of Tours, the celebration of Advent began in the fifth century when Bishop Perpetuus directed the start of fasting three times a week, from St. Martin’s Day on November 11 until Christmas. This is why Advent was sometimes also named Lent of St. Martin, and by the year 581, all of France was abiding by this practice. In fact, more devout followers fasted every day.
In the 13th century, the fast of Advent was not commonly practiced although it was still generally observed. It was then limited to the period from the feast of Saint Andrew on November 30, until Christmas Day, and falls on the Sunday closest to St. Andrew’s Day, or the fourth Sunday before Christmas.
The liturgy of Advent remained unchanged until the Second Vatican Council introduced minor changes, differentiating the spirit of Lent from that of Advent, emphasizing Advent as a season of hope for Christ’s resurrection.