The first mention of a preparatory period before Christmas is mentioned in a decree of the Council of Saragossa (380). The Council Fathers stated that every Christian should daily go to church from December 17 until the Theophany (January 6th). At the Synod of Mac (581) in Gaul (present day France) it was decreed that from November 11, the day of St. Martin, until December 24 every Christian should fast three times a week (Monday, Wednesday, Friday).
Our pre-Nativity period of preparation developed rather late. Scholars do not agree about the exact time it began. Some hold that it began in the sixth century. Others believe it began in the seventh or eighth century. The present liturgical pre-Nativity season was finally established at the Council of Constantinople (1166). The Council decreed that the fast would begin on November 15 and last until December 24 inclusive. Thus, there was created another 40 day fast.
The pre-Nativity fast is often called “Philip’s Fast” because it begins on the day after the feast of St. Philip. The fast was introduced to prepare the Church for a worthy celebration of the great and holy day of the Birth of Christ. The regulations for the fast were far more lenient than the Great Fast before Pascha. Only Monday, Wednesday, and Friday were days of strict fasting without meat, dairy products or oil (in Slavic countries). On Sundays fish was permitted. Lay people were at first permitted to eat fish on other days, too, until the monastic rigoristic influence prevailed.
It is interesting to observe that the famous 12th century Byzantine canonist Balsamon expressed the opinion that it would be enough if the lay people fasted only one week before Christmas. In 1958 a modern Greek author, Christos M. Enislides, welcomes Balsamon’s suggestion and believes that the best solution would be for the Church at large to abstain from meat and dairy products for 33 days; during the last seven days of the fast everybody should observe the strict fast. But for now this is a mere proposition and should not be seen as the rule.