Article: Chthonic gods such as Dis pater, the di inferi ("gods below"), and the collective shades of the departed (di Manes) were given dark, fertile victims in nighttime rituals. Animal sacrifice usually took the form of a holocaust or burnt offering, and there was no shared banquet, as "the living cannot share a meal with the dead". Ceres and other underworld goddesses of fruitfulness were sometimes offered pregnant female animals; Tellus was given a pregnant cow at the Fordicidia festival. Color had a general symbolic value for sacrifices. Demigods and heroes, who belonged to the heavens and the underworld, were sometimes given black-and-white victims. Robigo (or Robigus) was given red dogs and libations of red wine at the Robigalia for the protection of crops from blight and red mildew.

Now answer this question: When were the gods below and the dead celebrated?
nighttime