Mention must also be made of Al-Farra, the grammarian, and distinguished by his knowledge of grammar, philology, and various branches of literature. He died A.D. 822, at the age of sixty-three, and preceded both Mubarrad and Thalab, the latter of whom used to say: 'Were it not for Al-Farra, pure Arabic would no longer exist; it was he who disengaged it from the ordinary language and fixed it by writing.' At the request of the Khalif Al-Mamun he drew up in two years a most elaborate work, which contained the principles of grammar, and all the pure Arabic expressions which he had heard. It was entitled 'Al-Hudud' (the Limits or Chapters), and directly it was finished he commenced another in connection with the Koran, which is spoken of as a most wonderful production. He wrote besides several other works on grammar, and acted as tutor to the two sons of the Khalif Mamun. Though many other grammarians could be named, such as Al-Akhfash al Ausat, Abu Amr as Shaibani, Abu Bakr al Anbari, etc., none can be considered so celebrated as the persons above mentioned, who are regarded as the founders of the principles on which Arabic grammar has been established. In the middle of the third century of the Hijrah (A.D. 816-913), the Arabs first began to distinguish themselves as travellers and geographers. When Muslim Homeir was, in A.D. 845, ransomed from his captivity among the Byzantines and returned to his country, he wrote a book with the title of 'Admonitions on the Countries, Kings and Offices of the Greeks.' Forty years afterwards Jaafar bin Ahmed al Mervezi produced the first geographical work under the title of 'Highways and Countries,' which was followed by those of Ibn Foslan, Ibn Khordabeh, Jeihani, Al-Istakhri, Ibn Haukul, Al-Beruni, Al-Bekri and Idrisi. The great historian, Masudi, was also a writer of travels and an ambassador. Ibn Foslan was sent by the Khalif Muktadir (A.D. 908-932) to the King of the Bulgarians. Abu Dolaf, who accompanied an ambassador from China to the frontiers of that country, made, on his return, a report which Yakut afterwards embodied in his voluminous geographical Dictionary. A few details will be given about the six chief geographers and travellers of this period, viz., Ibn Khordabeh, Al-Istakhri, Ibn Haukul, Al-Beruni, Al-Bekri and Idrisi. As regards the first-named, it would appear that he has been the object of considerable controversies among the Orientalists of Europe. After employment in the post and intelligence departments in the provinces, he subsequently came to the court of the Khalif Motamid (A.D. 870-892), and became one of his privy councillors. He is the author of several works on various subjects, but his 'Geography,' says Sir H.M. Elliot, is the only work we possess of this author, and of this there is only one copy in Europe, in the Bodleian Library at Oxford. He died about A.D. 912.