According to Chinese written sources of 6th–8th centuries CE, Turkic tribes of Kazakhstan had oral poetry tradition. These came from earlier periods, and were primarily transmitted by bards: professional storytellers and musical performers. Traces of this tradition are shown on Orkhon script stone carvings dated 5th–7th centuries CE that describe rule of Kultegin and Bilge, two early Turkic rulers ("kagans"). Amongst the Kazakhs, the bard was a primarily, though not exclusively, male profession. Since at least the 17th century, Kazakh bards could be divided in two main categories: the zhıraws (zhiraus, žyraus), who passed on the works of others, usually not creating and adding their own original work; and the aqyns (akyns), who improvised or created their own poems, stories or songs. There were several types of works, such as didactic "termes", elegiac "tolgaws", and epic "zhırs". Although the origins of such tales are often unknown, most of them were associated with bards of the recent or more distant past, who supposedly created them or passed them on, by the time most Kazakh poetry and prose was first written down in the second half of the 19th century. There are clear stylistic differences between works first created in the 19th century, and works dating from earlier periods but not documented before the 19th century, such as those attributed to such 16th- and 17th-century bards as Er Shoban and Dosmombet Zhıraw (also known as Dospambet Žyrau; he appeared to have been literate, and reportedly visited Constantinople), and even to such 15th-century bards as Shalkiz and Asan Qayghı.