[I] From the conversion of the Roman empire to A. D. 900, with an account of the achievements and writings of the early Christian, Arab, and Chinese travelers and students.- [II] From the close of the ninth to the middle of the thirteenth century (C. A. D. 900-1260)- III. From the middle of the thirteenth century to the early years of the fifteenth century (C. A. D. 1260-1420)