According to Emperor of Dreams: A Clark Ashton Smith Bibliography (1978) by Donald Sidney-Fryer, "The Testament of Athammaus" was first published in the October 1932 issue of Weird Tales.

Athammaus then proceeds to relate how in his lifelong career as a headsman he has failed to successfully carry out his duty but once, this one failure causing Commoriom's downfall.

He tells of how news had come from the settlements near the Eiglophian Mountains of a murderous band of Voormi with their vile and bizarre hairless hybrid being named Knygathin Zhaum, who was rumored to be the product of the union of a Voormi and a being related to the deity Tsathoggua; furthermore, it was rumored that this being was invulnerable to any weapon and capable of escaping any form of imprisonment, which at the time Athammaus dismissed as only vulgar superstition.

This was all too much for Commoriom's citizens, who immediately began to depart in a mass exodus, leaving Athammaus and his men behind to do battle with the fiend; however, they realized that the rumours of Knygathin Zhaum being both immortal and uncontainable are true.

[2] Reviewing Out of Space and Time in the 1983 book The Guide to Supernatural Fiction, E. F. Bleiler remarked "Like certain other Hyperborean stories, with touches of grisly humor.