The 1911 Encyclopaedia Britannica characterises Baltistan as the western extremity of Tibet,[8] whose natural limits are the Indus river from its abrupt southward bend around the map point 35°52′N 74°43′E﻿ / ﻿35.86°N 74.72°E﻿ / 35.86; 74.72﻿ (Bend in the Indus course) and the mountains to the north and west. These features separate a comparatively peaceful Tibetan population from the fiercer Indo-Aryan tribes to the west. Muslim writers around the 16th century speak of Baltistan as the "Little Tibet", and of Ladakh as the "Great Tibet", emphasising their ethnological similarity.[8] According to Ahmad Hassan Dani, Baltistan spreads upwards from the Indus river and is separated from Ladakh by the Siachen glacier.[9] It includes the Indus valley and the lower valley of the Shyok river.[10]