Commoriom was the first capital of prehistoric Hyperborea in Clark Ashton Smith's fiction, established by pre-human migrants from the south. In its prime it was a grand city of marble and granite construction, with a skyline of altitudinous spires.
Its population eventually fled to found a new capital at Uzuldaroum. Two accounts survive: a legend that residents departed after the White Sybil of Polarion foretold destruction, and the headsman Athammaus's dispute of this, attributing the exodus instead to the loathsome depredations of the horrid outlaw Knygathin Zhaum.
Commoriom appears in Smith's "The Tale of Satampra Zeiros" (1931) and is referenced in Lovecraft's "At the Mountains of Madness," where the Elder Things' city is described as far older than the fabled Commoriom and Uzuldaroum.