The Day of the Dead celebrations in Mexico developed from ancient traditions among its pre-Columbian cultures. Rituals celebrating the deaths of ancestors had been observed by these civilizations perhaps for as long as 2,500–3,000 years.[10] The festival that developed into the modern Day of the Dead fell in the ninth month of the Aztec calendar, about the beginning of August, and was celebrated for an entire month. The festivities were dedicated to the goddess[11] known as the "Lady of the Dead", corresponding to the modern La Calavera Catrina.
By the late 20th century in most regions of Mexico, the practices had developed to honor dead children and infants on November 1, and to honor deceased adults on November 2. November 1 is generally referred to as Día de los Inocentes ("Day of the Innocents") but also as Día de los Angelitos ("Day of the Little Angels"); November 2 is referred to as Día de los Muertos or Día de los Difuntos ("Day of the Dead").