According to a document dating from the 18th century, Byatis is a great creature which resembles a horrific cross between a spider and a crab, with a single eye, a profusion of growths beneath its face "in the Fashion of some Sea Monster," the vicious claws of a crustacean, and a monstrous, trunk-like nose. In addition, it is possessed of a hypnotic gaze: looking into its great eye will force the victim into surrendering to the being's clutches. This text states that when the Romans came to Britain, they found Byatis locked behind an ancient stone door somewhere in the Severn Valley.
According to the De Vermis Mysteriis, Byatis originated somewhere in the gulf of space, and only came to earth later in its life. This text states that The Serpent-Bearded may be summoned merely by touching his image, and that after the beings known as Deep Ones arrived on our planet bringing their effigies of Byatis, they then called the deity here also. It was then imprisoned beneath the earth by entities unknown, although it is likely the Elder Gods had a hand in this.
When the Romans conquered Britain, they discovered Byatis in its sleeping place, and a group of legionaries formed a cult to the beast. Unfortunately, this cult was destroyed when their master briefly escaped from its containment and went on a rampage across the country. Hundreds of years later, the Normans built a castle on the place where Byatis lay dormant.
Sometime in the 1700s, a practitioner of the dark arts by the name of Sir Gilbert Morley (who may have himself been a vampire) gained control of The Berkeley Toad, and used its cosmic strength to augment his own. Morley let the beast loose at night to feed on the local townsfolk, but the more Byatis ate, the larger it became. Eventually, Byatis consumed Morley, and in doing so grew so large that it was unable to escape its prison, and so it remained chained there for the next two hundred and fifty years.
Come the twentieth century, and a man named Parry stumbled across Byatis's subterranean cell whilst seeking to disprove the legend of the Berkeley Toad, accidentally removing the seal placed there, but not quite releasing the beast. After running in abject terror, Parry later returned and set Byatis ablaze with a large amount of petrol, presumably destroying its physical form. However, at the last, Parry saw a great greenish cloud of eldritch mist coalesce into a colossal bat-winged toad-creature then fly away across the valley.
Byatis's current whereabouts are unknown, nor whether it actually still exists on this plane.
- The Shambler from the Stars (1935), by Robert Bloch.
- The Room in the Castle (1964), by Ramsey Campbell.
- The Beard of Byatis (1995), by Robert M. Price.