IO:

It seems that it is through Umar Khayyam’s Nowruznameh “the Book of the Nowruz,” that we have the close association of the festival with the calendar and the beginning of the Spring. Many of the rituals, traditions, and habits were also formed or appropriated after this point. The harvest festival of Chaharshanbe Suri (a fire festival) was incorporated into the Nowruz, although even today it only has a calendric proximity to the Nowruz and is largely an independent festival. Other Nowruz rituals were developed through social customs, including the visiting of the elders. The Haft Seen and the Sizdah Bedar, judging from their rather limited resonance, appear to be relatively recent traditions, most likely dating to the Safavid period.

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