time. Non-Zoroastrian accounts of typically Zurvanite beliefs were the first traces of Zoroastrianism to reach the west, which misled European scholars to conclude that Zoroastrianism was a dualist faith. The Zoroastrian cult of Zurvan should not be confused with the Manichaeism's use of the name Zurvan in Middle Persian texts to represent the Manichean deity of light. Mani had himself introduced this practice (for perhaps political reasons) in his Shapurgan, which he dedicated to his patron Shapur II. For much of the rest of the Sassanid era, the Manichaens were a persecuted minority, and Mani was sentenced to death by Bahram I. Calendar reforms Sacred fires The three great sacred fires of Persia at the time of the Sassanids were the Adur Farnbag, Adur Gushnasp and the Adur Burzen-Mihr which burnt in Pars, Media and Parthia respectively. Of these three the Adur Burzen-Mihr was the most sacred fire as it was linked to the prophet Zarathustra himself and king Vishtaspa. Mazdakite movement Avesta Middle Ages Arab conquest and under the Caliphate The Muslim conquest of Persia, also known as the Arab conquest of Iran led to the end of the Sasanian Empire in 651 and the eventual decline of the Zoroastrian religion in Iran. Arabs first attacked the Sassanid territory in 633, when general Khalid ibn Walid invaded Mesopotamia (what is now Iraq), which was the political and economic center of the Sassanid state. Following the transfer of Khalid to the Roman front in the Levant, the Muslims eventually lost their holdings to Iranian counterattacks. The second invasion began in 636 under Saad ibn Abi Waqqas, when a key victory at the Battle of Qadisiyyah led to the permanent end of Sasanian control west of Iran. The Zagros mountains then became a natural barrier and border between the Rashidun Caliphate and the Sassanid Empire. Owing to continuous raids by Persians into the area, Caliph Umar ordered a full invasion of the Sasanian Iranian empire in 642, which was completed with the complete conquest of the Sasanians around 651 The quick conquest of Iran in a series of well coordinated multi-pronged attacks, directed by Caliph Umar from Medina several thousand kilometres from the battlefields in Iran, became his greatest triumph, contributing to his reputation as a great military and political strategist. Iranian historians have sought to defend their forebears by using Arab sources to illustrate that "contrary to the claims of