A story of pre-Islamic Persian origin which is found in the great epico-historical poems of Shahnameh and is based on a true story that was further romanticized by Persian poets. The story chosen by Nezami, was commissioned and dedicated to the Seljuk Sultan Toghril II, the Atabek Muhammad ibn Eldiguz Jahan Pahlavan and his brother Qizil Arsalan. It contains about 6,500 distichs in length, the story depicts the love of Sassanian Khosrow II Parviz towards his Armenian princess Shirin. "Khusrow and Shirin" recounts the story of King Khosrow's courtship of Princess Shirin, and vanquishing of his love-rival, Farhad. The story has a complex structure with several genres exploited simultaneously; and contains many verbal exchanges and letters, all imbued with lyrical intensity. Khosrow endures long journeys, physical and spiritual, before returning to Shirin, his true love. The influence of Vis o Ramin is visible as the poem imitates a major scene (that of the lovers arguing in the snow) from Vis o Rāmin, as well as being in the same meter (hazaj) as Gorgāni's poem. Nezami's concern with astrology also has a precedent in an elaborate astrological description of the night sky in Vis o Rāmin. In turn, Nezami's great work had a tremendous influence on later authors and many imitations of this work were made. With complete artistic and structural unity, the epic of Khosrow o Shirin turned to be a turning point not only for Nizami but for all of Persian literature.