Mardi Gras originated as one of the series of carnival days held in all Roman Catholic countries between Twelfth Night, or Epiphany, and Ash Wednesday; these carnivals had their origin in pre-Christian spring fertility rites. The most famous modern Mardi Gras festivities are those held in New Orleans, La.; Rio de Janeiro, Brazil; Nice, France; and Cologne, Germany.
The first American Mardi Gras was celebrated near modern-day New Orleans on March 3, 1699. It wasn't until the mid-1800s did official parade organizations start to form with the Mystick Krewe of Comus in 1856 and the Krewe of Rex in 1872. The tradition is still carried on in New Orleans with many other krewes represented on floats in a myriad of parades. The official colors of Mardi Gras are purple, green and gold (representing justice, faith and power).
Mardi Gras celebrations can start as early as January 6, on the feast of Epiphany. The festivities end at midnight on Tuesday--the day before Ash Wednesday and the beginning of Lent. Mardi Gras day falls on any Tuesday between February 3 and March 9. Like Ash Wednesday, the date Mardi Gras falls on depends on the date of Easter--always occurring 46 days before Easter.