According to historians, the celebration of Mardi Gras has ancient roots in the pagan Roman celebration of Lupercalia. This was a February holiday and it honored the Roman god of fertility. It involved feasting, drinking, and carnal behavior.

However, with the rise of the Church in ancient Rome, Christian teaching and morals took root. The blending of tradition with new religious beliefs was a common practice in the ancient world and it helped people to transition away from paganism. In fact, there are a number of ancient Roman traditions that persevere in the Roman Catholic Church to this day, where they continue to guide the faithful.

What is less known about Mardi Gras is its relation to the Christmas season, through the ordinary-time interlude known in many Catholic cultures as Carnival. Carnival comes from the Latin words carne vale, meaning "farewell to the flesh" or “farewell to the meat”.

The Carnival season kicks off with the Epiphany, also known as Twelfth Night, Three Kings' Day and, in the Eastern churches, Theophany.

As Catholicism spread throughout Europe during the first millennium, different cultures celebrated the last day before Lent in their own ways, adapting the practices to suit their cultures. In France, the holiday became particularly popular as people feasted on foods that would be given up during the forty days of Lent. Meats, eggs, and milk were finished off in one day, giving the holiday its French title of ‘Mardi Gras’, which means Fat Tuesday. (The day is also known as Pancake Tuesday, from the custom of making pancakes to use up fat, eggs and dairy before the fasting and abstinence of Lent begins.)

As Europeans crossed the Atlantic to colonize the Americas, they brought their religious practices with them. From the onset, holidays such as Mardi Gras were celebrated in the colonies with as much enthusiasm as they were celebrated in Europe. As the colonies swelled with European immigrants, the celebrations went from the simple to the elaborate. In New Orleans, masked balls and public celebrations quickly became common. In fact, the celebrations became so popular that virtually everyone in the city joined in even if they were not Catholic.

However, in the late 18th century, the Spanish took control of New Orleans and having a more militant and serious perspective on the faith, they imposed significant restrictions on the holiday revelry. Among them, they banned masked balls. However, by 1823, this ban was lifted and parades returned by 1837. At this point, the celebration began to lose its identity as an exclusively Catholic tradition and became more secularized over the centuries.

In Louisiana, Mardi Gras in an official state holiday.

Mardi Gras Parade in New Orleans

In other parts of the world, the holiday became a season unto itself each branded with unique cultural practices. For example, Venice, Italy is famous for the masked balls that take place on Mardi Gras and the days before. The Venetian tradition dates back to the 13th century and the city remains a popular Mardi Gras destination today.

The official colors of Mardi Gras even have roots in Catholicism: purple, a symbol of justice; green, representing faith; and gold, to signify power.

Legend has it that the cakes were made in a circle to represent the circular routes that the Wise Men took to find Jesus, in order to confuse King Herod and foil his plans of killing the Christ Child.

In the early days, a coin or bean was hidden inside the cake, and whoever found the item was said to have good luck in the coming year. In Louisiana, bakers now put a small baby, representing the Christ Child, in the cake; the recipient is then expected to host the next King Cake party.

The day is also known as Shrove Tuesday (from "to shrive," or hear confessions), Pancake Tuesday and Fetter Dienstag.

Sources:
chefshalhoub.com/MardiGras.htm
catholic.org/lent/mardigras.php