Why do people, right before the beginning of Lent, celebrate Carnival with excessive eating and drinking, floats and processions, masks and merrymaking?
In Christian countries, Carnival is the last opportunity to eat and make merry before Lent, the 40 day period of fasting in preparation of Easter. Thus it is celebrated right before Ash Wednesday, the first day of Lent. "Mardi Gras" in New Orleans, for instance, means "Fat Tuesday". But since the 13th century the popular festival was begun ever earlier. The Carnival Season can now extend from right after Epiphany up to the eve of Ash Wednesday, basically coinciding with "Ordinary Time".
Thus Carnival is sometimes termed the Anti-Lent. In that sense the word can be interpreted as "carne vale", Latin for "farewell meat". Because it has this (psycho)logical connection to Lent, many churches are amenable to Carnival. In my Roman Catholic school in Belgium we were encouraged to dress up and bring candy and goodies.
But Carnival existed before Christianity, its pagan forms persisting well into the Christian era. When the Church couldn’t suppress it, it wisely adapted it to its own traditions. For instance, "carnival" really stems from "carrus navalis": the "naval car" or ship, which carried the Celtic and Germanic Sea-God from his Northern abode to the winter feasts. The medieval Church reinterpreted this as the Ship of Fools, on which all kinds of sinners sail to their death.
Such floats also rolled in Babylon, in honor of the God Marduk, and in Egypt, for Isis, the queen-goddess of life and light, who opens the year. Elements of this Isis-cult persevered in early Christianity (Isis was even connected to Mary). They point to Carnival’s nature as a celebration of the waning of winter, the return of a new year, and fertility.
Other elements derive from the Romans Saturnalia, a festival with lots of food and drink, dress-up and parades. The societal order was reversed and rules of behavior were suspended: higher classes had no authority over lower, masters waited on their slaves, men dressed like women. A temporary King was crowned and everyone had to abide by his most ludicrous whims. Even today, revelers elect a Prince Carnival.
Carnival, whether as Anti-Lent or pagan revelry, is thus a ritual of reversal and, at the same time, balance. Masks secure anonymity in this time of upheaval, which could sometimes end in bloody riots. Now that severe fasting is less (or not) on our agendas, there is less need for such excess. Still, the popularity of Carnival is outlasting the diminishing observation of Lent.