Valusia was the kingdom furthest to the west of the Thurian continent in the Thurian Age of Earth's pre-history. It was created and initially ruled by Serpent Men until they were overthrown by their human slaves. They attempted to control new human kingdom of Valusia from behind the scenes, using illusionary magic, when mankind's memories of the past wars faded but they were again defeated in a secret war. Finally they created a religion, the Snake Cult, to do the same thing again and almost succeeded. Their power was, however, eventually destroyed by Kull, an Atlantean barbarian who had gained the crown of Valusia by force.
Kull notes, in Robert E. Howard's The Shadow Kingdom that the Valusia of his time is a "fading, degenerate" country, "living mostly in dreams of bygone glory, but still a mighty land and the greatest of the Seven Empires". The kingdom is already ancient by his standards:
- "The hills of Atlantis and Mu were isles of the sea when Valusia was young."
The term Valusian can refer either to the Serpent Men or to the humans of Valusia.