From open sources

Orthodox Christians from November 28 to start the last of the long posts of the year – Christmas. It will last 40 days and will end on January 7 – the feast of the Nativity. Hence the name.

But it is worth noting that in fact the post names a few. It is also called Filippovka due to the fact that it starts right after memorial day St. Philip the Apostle, and Lent – because of the huge duration.

However, one thing is certain: the Nativity fast is the last multi-day post this year. He’s not the most strict, but has a number of features that are important.

The history of the establishment

The first mention of the Christmas post Dating from the IV century. In particular, it was talked about Pope Leo I (440-461) was: “within a year of the positions so laid out that the law of abstinence assigned for all times of the year, namely the post spring is in the lent and summer at Pentecost, and the autumn in the 7th, and the winter – in the 10th month.” Just winter of the four posts and was the precursor to the modern advent.

Interestingly, originally it lasted seven days, and then 10 and only at the Council of Constantinople in 1166 was approved for all Christians to keep fasting 40 days before Christmas.