Mardi Gras is a Christian holiday and popular cultural phenomenon that dates back thousands of years to pagan spring and fertility rites. Also known as Carnival or Carnaval, it’s celebrated in many countries around the world—mainly those with large Roman Catholic populations—on the day before the religious season of Lent begins. Brazil, Venice and New Orleans play host to some of the holiday’s most famous public festivities, drawing thousands of tourists and revelers every year.