 The days when the mundus was open were among the very few occasions that Romans made official contact with the collective spirits of the dead, the "Di Manes" (the others being Parentalia and Lemuralia).This secondary or late function of the "mundus" is attested no earlier than the Late Republican Era, by Varro.The jurist Cato understood the mundus' shape as a reflection or inversion of the dome of the upper heavens.