Carnival is the time of revelry and celebration that precedes the fast of Lent and culminates with Mardi-Gras, Fat Tuesday. Before the French Revolution it was the occasion for masquerades, and also raucous parades through the streets of Paris, like the promenade du bœuf gras ("fat ox.") A young boy, called "King of the Butchers" with a gilt crown, sword and scepter, rode the ox, at the sound of violins, fifes and drums, surrounded by butchers disguised as women.

Social barriers, good taste and rules of acceptable behavior fell by the wayside for a few days. The Church remonstrated in vain. The great writer Louis-Sebastien Mercier, who must receive credit for giving us the best snapshots of everyday life in Paris at the end of the 18th century, reports on the obscenity of the parades.

But the revelry was not limited to the streets of Paris. Versailles was not immune to the Carnival mood. A good example is the Bal des Ifs, where a cook could dance all night with a princess, and the King was attired in the same yew tree costume as seven other gentlemen.

A few decades later, a young Marie-Antoinette, lost in a whirlwind of entertainments at the beginning of her reign, would not miss the balls of the Opera during the Carnival season. She would mingle freely with the crowd, her identity thinly disguised by a mask and black domino, thus providing the pamphlet industry with ample fodder. For her participation in the festivities, see this excellent post by Elena.

All of this exuberance did not agree at all with the new tone of austerity that marked the Revolution. All Carnival celebrations were banned for indecency from 1790 through 1799. They resumed under Napoleon's reign, though in a far more subdued form. The "fat ox" had to wait a few years longer, until 1805, to be allowed again, and knew various eclipses during the 19th and 20th centuries. But It always regained its foothold and is still part of the Carnival celebrations in Paris.