贺兰山
Xiongnu writing, older than Turkic, is agreed to have the earliest known Turkic alphabet, the Orkhon script. This has been argued recently using the only extant possibly Xiongnu writings, the rock art of the Yinshan and Helan Mountains. Petroglyphs of this region dates from the 9th millennium BCE to the 19th century, and consists mainly of engraved signs (petroglyphs) and few painted images. Excavations done during 1924–1925 in Noin-Ula kurgans located in the Selenga River in the northern Mongolian hills north of Ulaanbaatar produced objects with over 20 carved characters, which were either identical or very similar to the runic letters of the Turkic Orkhon script discovered in the Orkhon Valley.