The Hyborian Age is an essay by Robert E. Howard pertaining to the Hyborian Age, the fictional setting of his stories about Conan the Cimmerian. It was written in the 1930s but not published during Howard's lifetime. Its purpose was to maintain consistency within his fictional setting.
The essay sets out in detail the major events of Howard's pseudohistorical prehistory, both period before and after the time of the Conan stories. In describing the end of the Thurian Age, the period described in his Kull stories, Howard links both sequences of stories into one shared universe. The names he gives his various nations and peoples of the age borrow liberally from actual history and myth. The essay also sets out the racial and geographical heritage of these fictional entities, making them progenitors of modern nations. For example, Howard makes the Gaels descendants of his own Cimmerians.
In addition to its use as underpinning to his Kull and Conan stories, Howard drew on his invented prehistory in tales with later settings. For instance, "Kings of the Night" brings King Kull forward in time to fight the Roman legions, while "The Haunter of the Ring," set in the modern age, makes use of a Hyborian artifact.
An unnamed Howard fragment published by Glenn Lord features two grave robbers, Allison and Brill, who discover in the Egyptian desert a structure older and different from anything they encountered before. Brill proposes that the structure is Stygian rather than Egyptian, and starts recounting the history of Stygia in nearly identical words to those used in the The Hyborian Age - but making no mention of the Hyborian kingdoms to the north of Stygia. Brill's source for the information is the Unaussprechliche Kulte (also known as Nameless Cults), a fictional work of Cthulhu Mythos arcane literature, cited in other Howard stories. This historical exposition seems an earlier draft, which Howard later extended greatly and dropped the grave robbers frame story.