元史
In the Chinese work "History of Yuan", Gerdkuh is recorded multiple times, as "Yü-r-gu", "K‘i-du-bu", "K‘i-du-bu-gu", and "Gir-r-du-k‘ie", on top of the mount "Yen-han", west of "Tan-han" (Damghan). The fortress is called "Tigado" by Hayton of Corycus.