the family of Farrokh Hormizd. Large parts of the region were conquered by the Kingdom of Armenia. Large parts of the region made up part of historical Armenia. The parts of historical Armenia within what is modern-day Azerbaijan comprise; Nor Shirakan, Vaspurakan, and Paytakaran. Vaspurakan, of which large parts were located in what is modern-day Iranian Azerbaijan is described as the cradle of Armenian civilization. On 26 May 451 AD, a very important battle was fought that would prove immensely pivotal in Armenian history. On the Avarayr Plain, at what is modern-day Churs (modern-day West Azerbaijan Province), the Armenian Army under Vardan Mamikonian clashed with Sassanid Persia. Although the Persians were victorious on the battlefield itself, the battle proved to be a major strategic victory for Armenians, as Avarayr paved the way to the Nvarsak Treaty (484 AD), which affirmed Armenia's right to practice Christianity freely. Heraclius, the Byzantine emperor, briefly held the region in the 7th century until peace was made with the Sassanids. After the Islamic Conquest of Iran, Arab invaders converted most of its people to Islam and made it part of the caliphate. Islamic period Sasanian and early Islamic period During the Arab invasion of Iran, the Spahbed of Iran was Rostam Farrokhzad, the son of Farrukh Hormizd, who was the son of Vinduyih, the uncle of Khosrau I and brother of the Sasanian usurper Vistahm. Rustam himself was born in Azerbaijan and led the Sasanian army into battle. He is also mentioned in the Shahnameh. The Sasanian army was defeated at the battle of al-Qādisiyyah and Rostam Farrokhzad, along with many other Sasanian veterans, was killed. In 642, Piruz Khosrow, one of the Sasanian survivors during the battle of al-Qādisiyyah, fought against the Muslims at Nahavand, which was a gateway to the provinces of Azerbaijan, Armenia and Caucasian Albania. The battle was fierce, but the Sasanian troops lost during the battle. This opened the gateway for the Muslims to enter Azerbaijan. The Muslims then invaded Azerbaijan and captured Isfandiyar, the son of Farrukhzad. Isfandiyar then promised, in return for his life, that he would agree to surrender his estates in Azerbaijan and aid the Muslims in defeating his brother, Bahram. Bahram was then defeated and sued for peace. A pact was drawn up according to which Azerbaijan was surrendered to Caliph Umar on usual terms of paying the annual Jizya. Muslims settled in Azerbaijan as