Today is Mardi Gras, Fat Tuesday, Shrove Tuesday. Mardi Gras is the culmination of the tradition Carnival Season, a time of celebration that actually predates Christianity. In Christian custom Carnival is most prominent in Roman Catholic countries, but it also makes an appearance in Orthodox countries such as Greece. The most famous celebration of carnival in Greece is in the town of Patras in the northern Peloponnese. It actually begins 4 days before Mardi Gras and finished on the Monday before that day.
Carnival was a time of celebration before the austere season of Lent. Feasting was almost a necessity so as to use up meat, eggs, butter and other animal products before fasting began. Most commonly it began on the third from last Sunday before Ash Wednesday, but in some places it began as early as the Feast of the Epiphany (Jan 6th in our calender).
Little of Carnival has survived the coming of Protestantism in England, except for the custom of "Pancake Day". Most of England's "Carnivals are held during the summer and fall. The southern, Catholic part of the Netherlands where it is called Karnaval, Carnaval or Vastenavond preserves the custom as do most countries in Eastern Europe. In Russia it preserves many of the traces of its pagan origin. Also, in many countries of the region Carnival has taken on some of the costume aspects that we in North America usually associate with Halloween. Needless to say this is true in many Latin countries as well.
It's in the Latin countries that Carnival has become the most famous. Portugal, Spain, Malta and Italy all share in the Carnival tradition. In all these places vestiges of the "inversion of society" still linger. In Tarragona in Catalonia, for instance, the effigies of the Carnival King and Queen are burnt at the end of festivities. In fact the festival of Carnival took many of its themes from the Feast of Fools that openly mocked the rulers, clerical and secular. This festival, usually held around New Year's had many elements dating directly back to the Roman feast of Saturnalia.
The most famous European Carnival is that of Venice, first recorded in 1268. Over the years the Venetian authorities many times tried to restrict the practices of Carnival such as the wearing of masks (though "society ladies" were sometimes required to wear masks during Carnivale so as to discourage the exhibition of costly jewelry). During much of the Middle Ages Venice was something of an "adult content Disneyland" during Carnivale. It took the decline of the Venetian Republic, Napoleon's conquest of Venice and the long grey rule of the AustroHungarian Empire to end the party. In the 1970s, however, local craftspeople began to manufacture the tradition pale carnivale mask known as the larva (Lating for "ghost") or volto (face). In 1979 an effort on the part of the Biennale, an international exhibit of contemporary and avant-garde art held every odd numbered year in Venice since 1895, and the Campagnia dei Grandi Alberghi (local hoteliers' association) relaunched Carnivale in Venice as one of the most popular events in Italy, and perhaps in all of Europe. Nowadays Venice, a city where tourists usually outnumber locals at any time of the year, becomes so crowded during the 10 days of carnivale that the causeway from the mainland has to be shut down because of the overcrowding. I don't speak of no place to sleep or eat. I speak of too little room to walk around.
In the Americas the Carnivals of Brazil, especially that of Rio de Janeiro, are the most famous. The Carnivales of the Caribbean, however, may be more festive. On some islands, such as Trinidad and Tobago, the celebrations may last a full month. Carnival is also celebrated in other parts of both South and Central America with varying amounts of enthusiasm and varying customs.
Here in Canada the Quebec City Winter Carnival is a descendant of the old celebrations, though it is held on the last days of January and early February so as to have good snow accumulations and cold enough temperatures for the ice sculptures. Winnipeg's Festival du Voyageurs is similarly held in early February for the same reasons.
The culmination of Carnival in Mardi Gras is not a universal feature of Carnival. In some places, particularly those with a longer carnival season other days of the festivity are more important. In Brazil, for instance, the season lasts two weeks. In New Orleans the celebration of Carnivale was introduced by the French settlers, but it became a multicultural event with traditions all its own. There are numerous "krewes", perhaps over 60 at the peak, which organize parades and other festivities during the two weeks preceding Ash Wednesday. The oldest parading krewes include those of "Rex: King of the Carnival"(from 1872) and Zulu (founded 1909). Both of these parade on Mardi Gas morning. The oldest of the night parading krewes is the Krewe of Proteus (1882) which organizes parades on the night of Lundi Gras (Fat Monday) . Numerous other Carnival celebrations are also held in the south eastern USA and even as far afield as Detroit.
For an overview of the subversive history of Carnival, the actual festival and other aspects of "collective joy" see Barbara Ehrenreich's new book 'Dancing in the Streets:A History of Collective Joy' (Metropolitan Books, NY, 2006). This book puts the whole matter into a comprehensive overview of what such festivities mean for society.