Though it is now a Christian and Catholic holiday, the exact origins of the celebration of the Carnival season may date back to a pre-Christian era in Ancient Greece or Rome, when pagan seasonal celebrations at this time of year were commonplace. The celebration of the specific Mardi Gras holiday as a Christian holiday may date back to medieval Europe during the Roman Catholic era, when the pagan festivals of Saturnalia and Lupercalia were likely repurposed for a new religious purpose. The process of converting a pre-existing holiday for new religious ideology was likely easier than simply banning the pagan festivals outright.
As far as specific celebrations are concerned, the New Orleans Mardi Gras, which is one of the most famous Mardi Gras celebration in the world, originated with the influx of European Catholics into the area during the 18th century. However, these celebrations remained mostly private in nature until the 19th century, when the first recorded public procession in celebration of Mardi Gras took place in 1837. The city's first Mardi Gras parade to feature early versions of modern-style floats took place 20 years later in 1857. This city's celebrations have direct roots in Mobile, Alabama, which is the site of the first major public Mardi Gras celebrations in the United States.