1. Introduction The NasirKhusraw Travelogue as the very first Farsi travelogue remaining from ٥, th century (more than 1000 years ago) has been subject of many studies in a variety of fields, including literature, historical and social studies, or even historical architect studies. Yet few studies have been carried out from linguistic viewpoint to show its capacities as a linguistic data source. The current study probes on relative clause extraposition and its motivations as a non-obligatory movement mostly based on functional and discourse criteria. In many languages, relative clause is mostly a clause that acts as a modifier for a head Np located in main clause. This modifier clause can appear right after (or based on the language word order before) the NP that is defined by the clause and in this case it is named canonical relative clause,Or it can be dislocated and be moved to the end of the sentence (named extraposed relative clause) Since there is no syntactic need to force this movement, the motivations of relative clause extraposition were explained to be discourse factors (Francis, 2010) such as Grammatical weight of clause (Hawkins, 1990 &2004), verb information Structure (Sheykho’, l Eslami, 2008) and a combination of some different factors together (Rasekh-Mahand et. al, 2012). 2. Materials and method Current study aimed to analyze the motivations of extrapositon relative clauses in historical proses. The NasirKhusraw Travelogue was studied and about 230 relative clauses were extracted based on systematic sampling which cover nearly more than half of the book. All relative clauses were grouped into 2 main categories based on their position in the sentence. 83 of them were in their canonical position (right after the head of NP they modify) and 138 were extraposed to the end of sentence after the main verb. 3. Results and discussion Comparing to present studies carried out by Rasekh-Mahand et. al, (2012) the rate of relative clause extraposition in The NasirKhusraw Travelogue is 3 times more than contemporary Persian texts (63% compared to 22%). All these extraposed relative clauses were analysed to figure out the head Np role in main and subordinate clause, and findings suggest that most extraposed clauses modify subject and object Np according to accessibility hierarchy (Keenan and Comrie. 1977) yet the top position is not occupied by Subject NP. 38% head NPs modified by extraposed relative clauses were Object NPs while 37% of them were Subject NPs which shows a little deviation of accessibility hierarchy in this book. Head Np definiteness was also studied in all extraposed relative clauses of The NasirKhusraw Travelogue. In Farsi, unlike some languages (Germany or English), there is no limitation on head Np definiteness and all types of NPs can be used in this position. However, only less than 3% of head NPs were pronouns. This means that although using pronoun as a head NP is not ungrammatical in Farsi, in NasirKhusraw Travelogue it was not very common. Head NP within relative clause in Farsi can appear in three different ways. It can be repeated completely, it can be referred to by a proper pronoun, or it can be omitted leaving a gap in relative clause instead. In The NasirKhusraw Travelogue using related pronoun in extraposed relative clause occurred 53%, using gap was second by 42% and, complete repetition was less than 6%. Verb information structure is another factor which was studied as a motivation for relative clause extraposition. It is supposed that when the verb of main clause has old-given information, it is most likely for the relative clause to be extraposed. Current study shows that in The NasirKhusraw Travelogue, more than 51% clauses were extraposed from the main clauses with linking verbs. These connecting verbs are supposed to bear old-given information. Last factor studied in this paper was relative clause grammatical weight. In Francis’, s (2010) work, grammatical weight refers to the length and/or complexity of a phrase in relation to the other phrases in the same sentence (Francis, 2010, P. 6) and it can be calculated by the number of verb immediate constituent to word-ratios (Francis, 2010, P. 12). The average length of extraposed relative clauses in The NasirKhusraw Travelogue was 6. 2913 and the average length of verb phrases was 1. 890. Grammatical weight of extraposed relative clauses in this book is 3. 3397. Compared to Rasekh-Mahand et al (2012), the grammatical weight is lighter in The NasirKhusraw Travelogue. 4. Conclusion In terms of the rate of extraposition, this criterion in The NasirKhusraw Travelogue is three times more than the contemporary Persian texts. Data also suggest a little deviation of accessibility hierarchy in terms of head NP position in this book as far the top position is not occupied by Subject NP but by Object NPs. The use of pronouns as the head NP was not very common in NasirKhusraw Travelogue, although it is not ungrammatical in Farsi. From the point of the grammatical weight factor, extraposed relative clauses in this book are lighter than the contemporary text. Finally, even though previous studies consider Farsi as a language that obligates gaps in the subject position, the NasirKhusraw Travelogue shows some examples of resumptive pronouns in the subject relative clause extraposition.