Kadatheron (not to be confused with Kadath) is a city in the land of Mnar on the River Ai in the Dreamlands. It was built by the same wandering tribes that built the Mnaran cities of Thraa, Ilarnek, and Sarnath. Sarnath eventually conquered the neighboring cities and lands (including Kadatheron) and forged an empire. (HPL: "The Doom That Came to Sarnath")
Kadatheron is a repository of lore written on brick cylinders pertaining to the city of Ib and its nonhuman inhabitants. The cylinders record how the Ibians arrived on Earth after they descended one night from the moon. (HPL: "The Doom That Came to Sarnath")