New Orleans' carnival season -- which starts on Twelfth Night and runs for the six weeks or so until Ash Wednesday -- is unlike any other in the world. Though the name is used to define the entire season, Mardi Gras itself, French for "Fat Tuesday," is simply the culmination of a whirl of parades, parties, street revels and masked balls, all inextricably tied up with the city's labyrinthine social, racial and political structures.

Mardi Gras was introduced to New Orleans in the 1740s, when French colonists brought over the European custom, established since medieval times, of marking the imminence of Lent with masking and feasting. Their slaves, meanwhile, continued to celebrate African and Caribbeanfestival traditions, based on musical rituals, masking and elaborate costumes, and the three eventually fused. From early days carnival was known for cavorting, outrageous costumes, drinking and general bacchanalia, and little has changed. However, although it is the busiest tourist season -- when the city is invaded by millions -- Mardi Gras has always been, above all, a party that New Orleanians throw for themselves.

It was in the mid-nineteenth century that official carnival took its current form, with the appearance in 1857 of a stately moonlit procession calling itself the Krewe of Comus, Merrie Monarch of Mirth. Initiated by a group of Anglo-Americans, the concept of the "krewes," or secret carnival clubs, was taken up enthusiastically by the New Orleans aristocracy. Nowadays about 60 official krewes equip colorful floats, leading huge processions on different -- often mythical -- themes. 

Tourists are less likely to witness the Mardi Gras Indians, African-American groups who, in their local neighborhoods, organize themselves into "tribes" and, dressed in fabulous beaded and feathered costumes, gather on Mardi Gras morning to compete in chanting and dancing. As in Sydney and Rio, the gay community also plays a major part in Mardi Gras, particularly in the French Quarter, where the streets teem with strutting drag divas.

One important New Orleans Mardi Gras ritual is the flinging of "throws" from the floats. Teasing masked krewe members scatter beads, beakers and doubloons (toy coins) into the crowds, who beg, plead and scream for them. Anyone keen to see the show should head for Bourbon Street.

The two weeks leading up to Mardi Gras are filled with processions, parties and balls, but excitement reaches fever pitch on Lundi Gras, the day before Mardi Gras. 

The fun starts early on Mardi Gras day, with walking clubs striding through uptown accompanied by raucous jazz on their ritualized bar crawls. The fun continues throughout the Quarter and the Faubourg until midnight, when a siren wail heralds the arrival of a cavalcade of mounted police that sweeps through Bourbon Street and declares through megaphones that Mardi Gras is officially over.