Article: While christian festivals such as corpus christi were church-sanctioned celebrations, Carnival was also a manifestation of European folk culture. In the Christian tradition the fasting is to commemorate the 40 days that Jesus fasted in the desert according to the New Testament and also to reflect on Christian values. As with many other Christian festivals such as Christmas which was originally a pagan midwinter festival, the Christian church has found it easier to turn the pagan Carnaval in a catholic tradition than to eliminate it.  Unlike today, carnival in the Middle Ages took not just a few days, but it covered almost the entire period between Christmas and the beginning of Lent. In those two months, several Catholic holidays were seized by the Catholic population as an outlet for their daily frustrations.

Now answer this question: What pagan midwinter festival did the church find easier to subvert than eliminate?
Christmas