^Haug, Robert (27 June 2019). The Eastern Frontier: Limits of Empire in Late Antique and Early Medieval Central Asia (بە ئینگلیزی). Bloomsbury Publishing. p. 65. ISBN978-1-78831-722-1. The collapse of the Hephthalite domains made neighbours of the Türk Khāqānate and the Sasanian Empire, both sharing a border that ran the length of the River Oxus. Further Turkish expansion to the west and around the Caspian Sea saw them dominate the western steppes and its people and extend this frontier down to the Caucasus where they also shared a border with the Sasanians. Khusrow is noted at the time for improving the fortifications on either side of the Caspian, Bāb al-Abwāb at Derbent and the Great Wall of Gorgān.
^Taagepera, Rein (1979). "Size and Duration of Empires: Growth-Decline Curves, 600 B.C. to 600 A.D.". Social Science History. 3 (3/4): 129. doi:10.2307/1170959. JSTOR1170959.
^Taşağıl, Ahmet (2021). Türk Model Devleti Gök Türkler. Bilge Kültür Sanat. ISBN9786059521598.
^West, Barbara A. (19 May 2010). Encyclopedia of the Peoples of Asia and Oceania. Infobase Publishing. p. 829. ISBN978-1-4381-1913-7. The first people to use the ethnonym Turk to refer to themselves were the Turuk people of the Gokturk Khanate in the mid sixth-century