Following the collapse of the Sassanid Empire and the subsequent rise of Islam in the region, the Kayanian legends fell out of favour until the first revival of Iranian culture under the Samanids. Together with the folklore preserved in the Avesta, the "Khwaday-Namag" served as the foundation of other epic collections in prose, such as those commissioned by Abu Mansur Abd al-Razzaq, the texts of which have since been lost. The Samanid-sponsored revival also led to the resurgence of Zoroastrian literature, such as the Denkard, book 7.1 of which is also a historiography of Kayanians. The best known work of the genre is however Firdowsi's "Shahnameh" "Book of Kings", which - though drawing on earlier works - is entirely in verse.