Clark Ashton Smith (CAS) dedicated this poem to Mamie Lowe Miller, who died in 1917. He said of her (in a letter to George Sterling*):
My best friend here is very ill. She seems to have developed an attack of brain fever in addition to the consumption from which she has suffered for years. I don't know whether she will live or not. If she dies, I think I will go mad with grief and a guilty conscience.
Fittingly, he titled the poem with the Latin phrase for "Rest in peace".
My favorite stanza from this very moving poem also happens to have a significant typo as captured on The Eldritch Dark, so here's the complete text of that stanza with the corrected word noted in bold:
Pass, with the music flown
From ivory lyre, and lute
Of mellow string left mute
In cities desolate ere the dream of Tyre.
The phrase "Of mellow string left mute" beautifully renders the passing of a human life as the silencing of music - a notion not unique to CAS, but rarely expressed with more feeling.
*See letter #154 in in The Shadow of the Unattained: The Letters of George Sterling and Clark Ashton Smith published by Hippocampus Press.