原指贝加尔湖的瀚海, 至盛唐后同时具三种含义: 贝加尔湖、天池、沙漠。瀚海变为西部沙漠的代称, 是武则天时期领瀚海都督一职的回纥部族短暂西迁留下的痕迹; 随后瀚海军府在庭州设立, 又使瀚海与西域相关联。元代称杭爱山为瀚海, 是当地居民沿用唐瀚海都督府所在地名山。明清时瀚海为大沙漠的专称。

As a place name of the frontier, Hanhai had been referred to the Lake Baikal. Till the prosperous period of Tang Dynasty, it added to other two meanings, namely, "vast desert" and "pool on the top of the Tianshan Mountain" (Heavenly Lake). During the period ruled by Empress Wu Zetian of the Tang Dynasty, the Huihe (an ancient Chinese tribe), whose headman held the post of military govemor of Hanhai, migrated westwards so that Hanhai gradually became a substitute name for the westem desert. Subsequently, the Hanhai army stationed at Tingzhou, which related Hanhai to the western region. Under the Yuan Dynasty the Hang' aishan Mountain was named as Hanhai by local Huihe residents, because the Hanhai military prefecture of Tang Dynasty had ever been established there. And during the period of Ming- Qing dynasties, Hanhai became a special name of desert.