around 500 C.E., while the cursive script develops approximately a century later. The cursive script is thus named because its letters are connected with a base line. Since many letters in the cursive script are extremely similar in form, to the point of being indistinguishable, it is the most difficult to read of the three varieties. As the Sogdian alphabet became more cursive and more stylized, some letters became more difficult to distinguish, or were distinguished only in final position, e.g. n and z. Source materials The Sogdian script is known from religious texts of Buddhism, Manichaeism, and Christianity, as well as from secular sources such as letters, coins, and legal documents. The oldest known Sogdian documents are the Ancient Letters, found in 1920 by Sir Aurel Stein in a watchtower near Dunhuang, China. These letters date to approximately 312-313 C.E. and are written in Early Sogdian. The Sogdian Buddhist texts, written in the sutra script, are younger, dating to approximately the sixth to eighth or ninth century. They were found during the first two decades of the twentieth century in one of the caves of the Thousand Buddhas in the Chinese province of Gansu. The bulk of these manuscripts reside in the British Library, the Bibliothèque nationale de France, and the Russian Academy of Sciences. Another important discovery was of the Mug Documents in 1933 by Soviet scholars. These documents were found in the remains of a fortress on Mount Mug in northern Tajikistan. The documents, numbering over 76, were written on many different types of materials, such as paper, silk, wood, and skin. According to the dates on the documents, they date to the eighth century C.E. The majority of them were written using the Sogdian cursive script. Child writing systems The "Uyghur" cursive script eventually developed into the Old Uyghur alphabet, which was used to write the Old Uyghur language. This child script was, however, rotated 90 degrees, written in a vertical direction from top to bottom, but with the first vertical line starting from the left side, not from the right as in Chinese, most probably because the right-to-left direction was used in horizontal writing. The Traditional Mongolian alphabet, being an adaptation of the Old Uyghur alphabet, still uses this kind of vertical writing, as does its more remote descendant Manchu. Unicode In Syriac script, three additional characters were used to represent sounds of Sogdian that