The Blood of Belshazzar is a story in the Cormac Fitzgeoffrey series about a knight fighting in the Crusades. Cormac Fitzgeoffrey only appears in two of these tales: Hawks of Outremer and The Blood of Belshazzar, both written in 1931. In the latter, Cormac seeks help in rescuing his leader from barbarians even more fierce and evil than those that hold his friend captive.

The story sold for $115 to Oriental Stories.

He refers to the story in a letter (#149) to his friend Tevis Clyde Smith, circa December 1930:

I’ve sold nothing recently except a tale to Oriental Stories and one to Weird Tales. The Oriental story I feel I sold merely on my reputation — if I can be said to have one. The title, “The Blood of Bel-Shazzer,” referring to a jewel, was the only interesting thing about it. The plot was hackneyed and sketchy, the action labored and artificial. Only once in the entire story did I evoke a slight spark of the fire that has smoldered out in me. But at least I sold it, for $115.

Howard also mentions the story in a letter (#169) to HPL in June 1931:

Yet I certainly show no trace of Oriental blood — thank God. Strangely enough, something like you mentioned, I feel a dim sense of a vast epoch lurking behind the East of the early ages — a sort of huge lurking night behind the dawn represented by Egypt and by Babylon — a dim sense of gigantic black cities from whose ruins the first Babylon rose, a last mirrored remnant of an age lost in the huge deep gulf of night. I have touched on this briefly in a story titled “The Blood of Belshazzer” which Mr. Wright accepted for Oriental Stories.

And again here's an extract from a letter (#183) Howard wrote to Tevis Clyde Smith in November 1931:

I’m glad you liked the Oriental story; I take it you are referring to the Belshazzar tripe. Personally, I thought it was pretty rotten in spots, particularly towards the conclusion when I had to drag in so blasted much explanation.