The album was initially named På svarte troner (Norwegian for "On Black Thrones") but was renamed shortly before its release.

The song "Det som en gang var" (with a slightly different spelling) would appear on the next album, Hvis lyset tar oss.

The album cover is visually inspired by the Advanced Dungeons & Dragons (1st edition) module The Temple of Elemental Evil.

Det som engang var was reissued in 1994, by Misanthropy Records, in two formats: CD and vinyl.

Eduardo Rivadavia of Allmusic wrote: "Vikernes' claim to musical genius would soon be irreparably stained by his, shall we say, extra-curricular infamy, burying all of the fascinating contradictions inherent in his art under the brutally one-dimensional label of 'murderer', and, by extension, forcing complicated feelings of guilt upon all those who would dare experience this otherwise compelling music.