Kingdom of Axum in modern Ethiopia, and Eritrea. Included in his work Christian Topography were some of the earliest world maps. Though Cosmas believed the earth to be flat, most Christian geographers of his time disagreed with him. Syrian bishop Jacob of Edessa (633–708) adapted scientific material sourced from Aristotle, Theophrastus, Ptolemy and Basil to develop a carefully structured picture of the cosmos. He corrects his sources and writes more scientifically, whereas Basil's Hexaemeron is theological in style. Karl Müller has collected and printed several anonymous works of geography from this era, including the Expositio totius mundi. Islamic world In the latter 7th century, adherents of the new religion of Islam surged northward out of Arabia taking over lands in which Jews, Byzantine Christians and Persian Zoroastrians had been established for centuries. There, carefully preserved in the monasteries and libraries, they discovered the Greek classics which included great works of geography by Egyptian Ptolemy's Almagest and Geography, along with the geographical wisdom of the Chinese and the great accomplishments of the Roman Empire. The Arabs, who spoke only Arabic, employed Christians and Jews to translate these and many other manuscripts into Arabic. The primary geographical scholarship of this era occurred in Persia, today's Iran, in the great learning center the House of Wisdom at Baghdad, today's Iraq. Early caliphs did not follow orthodoxy and so they encouraged scholarship. Under their rule, native non-Arabs served as mawali or dhimmi, and most geographers in this period were Syrian (Byzantine) or Persian, i.e. of either Zoroastrian or Christian background. Persians who wrote on geography or created maps during the Middle Ages included: Al-Khwārizmī (780–850) wrote The Image of the Earth (Kitab surat al-ard), in which he used the Geography (Ptolemy) of Ptolemy but improved upon his values for the Mediterranean Sea, Asia, and Africa. Ibn Khurdadhbih (820–912) authored a book of administrative geography Book of the Routes and Provinces (Kitab al-masalik wa’l-mamalik), which is the earliest surviving Arabic work of its kind. He made the first quadratic scheme map of four sectors. Sohrab or Sorkhab (died 930) wrote Marvels of the Seven Climes to the End of Habitation describing and illustrating a rectangular grid of latitude and longitude to produce a world map. Al-Balkhi (850–934) founded the "Balkhī school" of terrestrial mapping in Baghdad. Al-Istakhri (died 957) compiled the Book of the Routes of States, (Kitab Masalik al-Mamalik) from personal observations and literary