1. Introduction
Persian language had been prevailed by various factors in Anatolia, and had been the official and administrative language of there for more than five centuries; therefore, the most important aspect of Iran's cultural relations with Anatolia is the penetration and expansion of Persian language and literature in the region.
The first stage of this process began by the conquest of the Great Seljuks on the Byzantine Empire’s territory in this area (463 AH), and continued to the end of the Great Seljuk period (552 AH). This stage, in fact, was still in the genesis. During this course, there were still no other influential factors affecting the development of Persian language. The conquest of the Great Seljuks on the Byzantine Empire was in some way as a result of the Seljuk sultans being influenced by the Iranian political and cultural traditions under the Iranian bureaucrats. Therefore, the role of the bureaucratic class in this case has special significance.
2. Methodology
By using descriptive-analytic method, this article seeks to study the function and role of the bureaucratic system in the development of Persian language in Anatolia only during the Great Seljuk period, while explaining the bureaucratic system of the Great Seljuk tribes and the place of the Persian language in this system. The paper will answer the question of how Persian language was expanded in Anatolia? And what role did Khwaja Nizām- al-Mulk play in this field?     
 
3. Discussion
The Seljuk dynasty belonged to the tribes of Oghuz, who lived in the northern shores of Jaxartes, which they migrated to Transoxania and Khorasan at the end of the fourth century. They dominated Khorasan by crushing the Ghaznavid army in several times before 431/1040. Then, an alliance was created between the Iranian bureaucrats and the Seljuk Turkmens as a result of the unfamiliarity of the Seljuks with the managerial customs of the civilized regions and the frustration of the Iranian officials from the Ghazni court. Hence, by establishing a firm bond between the Persian officials with the Seljuks, the Persian language was also widely spread wherever the Seljuk’s domination was widespread.
Among these officials, Khwaja Nizām- al-Mulk has the most influence on the formation, strengthening and consolidation of the Seljuk bureaucratic system and on the expansion of their territory. At first, he arrived at the court of Chaghri beg, and later, he became the Vizier (Prime Minister)  of Alp Arsalan, and he founded the rule of Alp Arsalan by the suppression of sultan’s rivals, and over the course of ten years, he was the Prime Minister. After the death of Alp Arsalan, despite the existence of many claimants for the monarchy, Khwaja Nizām- al-Mulk placed Malikshah on the throne, and he himself was appointed his Vizier and took the title of Atabak. So, he was in charge of the ministry for thirty years. He was the main administrator of the Seljuq rule and guarantor of the discipline of their territory, who led the Turkmen tribes to the Christian regions of the Caucasus and Anatolia for regulating the relations between Turkmen and the Seljuq monarchy. The ultimate goal of this policy can be found in his words, which if the Turkmens won, "a province would be added to the Seljuk’s countries and, if they were killed, the government would be at ease". Nizam al-Mulk encouraged Turkmens to be present in the western frontiers. He, also, forced the displacement of some tribes in those areas.
The Turkmens' migration to Anatolia and their systematic advance in Byzantium led to the severe reaction of the Byzantine Emperor, who took care of the invading Turkmens. Turkmens sought help from the Seljuqid Sultan, and the Sultan also supported them, and in 461 AH/1071, he countered Byzantine Emperor and imprisoned him in a heavy defeat in Malazgird. After taking the eastern part of the Byzantine Empire and obtaining a certain tribute, he tried to liberate Emperor and restore him. As a result of the battle, in addition to healing the relationship between Turkmens and the Seljuqid Sultan, the Seljuq territory was developed and the way was paved for the establishment of Turkmen (now almost loyal to the Sultan) in Anatolia. These lands were handed over to the Turkmen emirs by the Central Court. According to available evidence, they were subordinate to the Seljuk Sultan and regarded themselves as the vassal 'Moqta' under the Seljuk sultan. Therefore, the Central Office was able to organize and monitor the administrative situation of the region in these newly taken areas.
By existing evidence, Nizam al-Malik had used Persian as the only official language of the Seljuk bureaucratic system, and it seems that it remained the official language until the end of his rule. According to Nizam al-Mulk's regulations in order to consolidate the administrative system and the rule of the Seljuks in the Anatolian region, Persian language also found place in these regions by the administrative agents, because he deployed a large number of Iranian agents and, since these agents were Persian, this language became the administrative and official language in Anatolia. This situation transformed Anatolia into one of the most important centers of support for Persian poets and poets after the Mongol invasion
4. Conclusion
At the beginning of their migration to Iran, Seljuks brought a large number of Turkmen tribes to the country. Being influenced by Iranian political-administrative thought, they were led to create a centralized government similar to the Iranian model, but, reserving the previous tribal ideas, the Turkmen tribes became a decentralized force. Since the time of Alp Arsalan, the Seljuq sultans, in addition to many other factors, have been influenced by the Iranian bureaucrats, and at the head of them, Khwaja Nizam al-Mulk, to emigrate to Anatolia in order to get rid of the negative results of this decentralized trend of Turkmen.
By the migration of these tribes and the full support of Seljuk sultan and Nizām- al-Mulk, before, during and after the battle of Malazgird,  they took a large part of Anatolia from the Byzantine Empire and added it to the Seljuk territory. On the other hand, the Shafi’i Khwaja Nizām- al-Mulk, as the actual founder of the Seljuk regime, placed the Persian language as the dominant and official language of this bureaucratic system, and by founding the Schools of 'Nizamia', he tried to cultivate the Shāfi’ī religious bureaucrats, who were able to develop and continue his thoughts about the bureaucratic system. Due to Sultan Alp Arsalan and Malikshah's inexperience,  Khawaja Nizām- al-Mulk, who had been the Vizier for 30 years, took responsibility for all the political, military, administrative, economic and cultural affairs.
After the conquest of Anatolia, Khwaja developed the Seljuk bureaucratic-administrative system by sending official agents to administer the new occupied territory in Anatolia. Along with the expansion of the administrative system, the Persian language, also, became popular in Anatolia, because it had become the official and administrative language of the Seljuk territory due to his and other bureaucrats' efforts. This bureaucratic system was prevailed and consolidated in Anatolia, during the sixth century. Therefore, Persian became the official language of the region, which continued until several centuries later.
Key words: Bureaucratic system, Persian language, The Great Seljuks, Nizām-al-Mulk, Anatolia