Battle of Nahāvand The Battle of Nahāvand ( also Nihāvand or Nahāwand ) ( Arabic : معركة نهاوند ) Battle of Nahāwand was fought in 642 between Arab Muslims and Sassanid armies . The battle is known to Muslims as the " Victory of Victories . " The History of Tabari mentions that Piruzan , the officer serving the Persian King Yazdgerd III had about 100 , 000 men , versus a Muslim army of about 30 , 000 - 100 , 000 . The Persians were outmanoeuvered , trapped in a narrow mountain valley , and lost many men in the ensuing rout . Yazdegerd escaped to the Merv area , but was unable to raise another substantial army . It was a decisive victory for the Rashidun Caliphate and the Persians consequently lost the surrounding cities including Sephahan ( renamed Isfahan ) . The Khan of the Turks later lent him some soldiers , but the soldiers mutinied in the year 652 . The former Sassanid provinces , in alliance with Parthian and White Hun nobles , resisted for a few more years in the region south of the Caspian Sea , even as the Rashidun Caliphate was replaced by the Umayyads , thus perpetuating the Sassanid court styles , Zoroastrian religion , and Persian speech . Various versions are told about Nahāvand and how the battle was ensued in the early stages . Some note that the Muslim Arabs managed to deceive the Persians through a ruse , that Caliph Omar had died . The Persian cavalry , full of confidence mounted an ill - prepared pursuit of the bedouins who swiftly retreated to a safe area and eventually surrounded and trapped the Persian force before assailing it from all sides , and decisively defeating it . As the historian Tabari mentions , the Persians were never again able to unite their men in such numbers and many were already talking of dissolving the Empire and going their separate ways when the battle was commencing . Many of Yazdegerd ' s military and civilian officials had abandoned him . Nahāvand marked the dissolution of the Sassanian Imperial army , with the fall of the last of the grand marshals of the army and the rise of warlord ism among the Persians . The Emperor Yazdegerd III attempted to raise troops by appealing to other neighbouring areas such as the princes of Tukharistan and Sogdia and eventually sent his son Peroz III to the Tang court , but without any success . Yezdegerd hurriedly fled towards the east where he was ill - treated by several Marzban ( provincial governors ) in the north as well as in Merv , where the governor Mahoye openly showed his hostility to the Emperor . According to non - Muslim sources , Yazdegerd failed to rally enough support in Eastern Persia where the Sassanians were unpopular with the locals . Muslim sources like Tabari reported that the province of Khorasan revolted against Sassanian rule , just as it had years earlier when it had sided with Khosrau II ' s uncle Vistahm . When Yazdegerd was crowned in Estakhr , Persia had in fact three Kings ruling in different regions and this province had not given its support to Yazdegerd at first . Before Yazdegerd had a chance to receive help from the Hepthalites and Turkish tribes , he was assassinated by a local miller in Merv in 651 . Thereafter , Yazdegerd ' s , son Peroz III , attempted to re - establish the Sassanid empire against the Rashidun Caliphate and its successor , the Umayyad Caliphate , though the plan did not develop , as Peroz III ultimately died in China .