to Magadha (modern northeastern India) during the 7th century. Afterwards he wrote the book Zhang Tian-zhu Guo Tu (Illustrated Accounts of Central India), which included a wealth of geographical information. Chinese geographers such as Jia Dan (730–805) wrote accurate descriptions of places far abroad. In his work written between 785 and 805, he described the sea route going into the mouth of the Persian Gulf, and that the medieval Iranians (whom he called the people of the Luo-He-Yi country, i.e. Persia) had erected 'ornamental pillars' in the sea that acted as lighthouse beacons for ships that might go astray. Confirming Jia's reports about lighthouses in the Persian Gulf, Arabic writers a century after Jia wrote of the same structures, writers such as al-Mas'udi and al-Muqaddasi. The later Song dynasty ambassador Xu Jing wrote his accounts of voyage and travel throughout Korea in his work of 1124, the Xuan-He Feng Shi Gao Li Tu Jing (Illustrated Record of an Embassy to Korea in the Xuan-He Reign Period). The geography of medieval Cambodia (the Khmer Empire) was documented in the book Zhen-La Feng Tu Ji of 1297, written by Zhou Daguan. Middle Ages Byzantine Empire and Syria After the fall of the western Roman Empire, the Eastern Roman Empire, ruled from Constantinople and known as the Byzantine Empire, continued to thrive and produced several noteworthy geographers. Stephanus of Byzantium (6th century) was a grammarian at Constantinople and authored the important geographical dictionary Ethnica. This work is of enormous value, providing well-referenced geographical and other information about ancient Greece. The geographer Hierocles (6th century) authored the Synecdemus (prior to AD 535) in which he provides a table of administrative divisions of the Byzantine Empire and lists the cities in each. The Synecdemus and the Ethnica were the principal sources of Constantine VII's work on the Themes or divisions of Byzantium, and are the primary sources we have today on political geography of the sixth-century East. George of Cyprus is known for his Descriptio orbis Romani (Description of the Roman world), written in the decade 600–610. Beginning with Italy and progressing counterclockwise including Africa, Egypt and the western Middle East, George lists cities, towns, fortresses and administrative divisions of the Byzantine or Eastern Roman Empire. Cosmas Indicopleustes, (6th century) also known as "Cosmas the Monk," was an Alexandrian merchant. By the records of his travels, he seems to have visited India, Sri Lanka, the