Bilad al-Sham. On the eve of the Arab Muslim conquests the Byzantines were still in the process of rebuilding their authority in the Levant, which had been lost to them for almost twenty years. At the time of the Arab conquest, Bilad al-Sham was inhabited mainly by Syrian Christian sects, Ghassanid and other local Arab tribes and Nabatean Arabs, as well as Greeks, and by non-Christian minorities of Jews, Samaritans, and Itureans Arabs. The population of the region did not become predominantly Muslim identity until nearly a millennium after the conquest. In Southern Levant The Muslim Arab army attacked Jerusalem, held by the Byzantines, in November, 636. For four months the siege continued. Ultimately, the Orthodox Patriarch of Jerusalem, Sophronius, agreed to surrender Jerusalem to Caliph Umar in person. Caliph Umar, then at Medina, agreed to these terms and traveled to Jerusalem to sign the capitulation in the spring of 637. Sophronius also negotiated a pact with Caliph Umar, known as the Umariyya Covenant or Covenant of Omar, allowing for religious freedom for Christians in exchange for jizya, a tax to be paid by conquered non-Muslims, called 'Ahl al Dhimmah'. While the majority population of Jerusalem during the time of Arab conquest was Christian, the majority of Palestine's population, according to contemporary Israeli references, about 300,000–400,000 inhabitants, was still Jewish. In the aftermath the process of Islamization took place, combining immigration to Palestine with the adoption of Arabic as the official language, and conversion of a part of the local Christian population to Islam. Rashidun Caliphate According to the historian James William Parkes, during the 1st century after the Arab conquest (640–740), the caliph and governors of Syria and the Holy Land ruled entirely over Christian and Jewish subjects. He further states that apart from the Bedouin in the earliest days, the only Arabs west of the Jordan were the garrisons. The Arab garrisons were kept apart in camps, and life went on much as before for the local population. The taxes instituted were the kharaj—a tax that landowners and peasants paid according to the productivity of their fields—as well as the jizya—paid by non-Muslims in return for protection under the Muslim state and exemption from military service. The Byzantine civil service was retained until a new system could be instituted; therefore, Greek remained the administrative language in the new Muslim territories for over 50 years after the conquests. Umayyad