In Zoroastrian tradition the longest and darkest night of the year was a particularly inauspicious day, and the practices of what is now known as “Shab-e Chelleh/Yalda” were originally customs intended to protect people from evil (see dews) during that long night,[rs 7] at which time the evil forces of Ahriman were imagined to be at their peak. People were advised to stay awake most of the night, lest misfortune should befall them, and people would then gather in the safety of groups of friends and relatives, share the last remaining fruits from the summer, and find ways to pass the long night together in good company.
The next day (i.e. the first day of Dae month) was then a day of celebration,[note 1] and (at least in the 10th century, as recorded by Al-Biruni), the festival of the first day of Dae month was known as Ḵorram-ruz (joyful day) or Navad-ruz (ninety days [left to Nowruz]).[rs 1] Although the religious significance of the long dark night has been lost, the old traditions of staying up late in the company of friends and family have been retained in Iranian culture to the present day.