Varg Vikernes recorded the first four Burzum albums between January 1992 and March 1993 at the Grieg Hall in Bergen. However, the releases were spread out, with many months between the recording and the release of each album. During this time, Vikernes became a part of the early Norwegian black metal scene and met Mayhem guitarist Euronymous. He also allegedly took part in burning down four churches, along with other members of the scene. In August 1993, Vikernes stabbed Euronymous to death outside his apartment in Oslo. He was arrested a few days later and, in May 1994, was sentenced to 21 years in prison for both the murder and the church arson.
The opening track on Filosofem, "Burzum", was the first song Vikernes wrote as Burzum. It had been recorded in September 1992 for the Hvis lyset tar oss album, but Vikernes was unhappy with it and re-recorded it for this album six months later. According to a statement made by Vikernes on burzum.org, the master tapes for the version of "Burzum" meant for Hvis lyset tar oss were lost by the Norwegian prison system.
The album was recorded under purposefully bad conditions in order to retain a raw lo-fi sound. No guitar amplifier was used; instead Vikernes plugged his guitar into the amplifier of his brother's stereo and used old fuzz pedals. For the vocals, he asked a sound technician for the worst microphone he had, and ended up using an old helicopter headset.
The music of Filosofem continued Vikernes' experimentation with minimalism, repetition, and ambient music within black metal. The tracks are all quite long (the shortest being just over seven minutes), and are typically composed around very few musical motifs. For instance, "Jesu død", a track of over eight-and-a-half minutes, is primarily based around variations of a single riff. The epic "Rundtgåing av den transcendentale egenhetens støtte", Burzum's longest ambient song to date, repeats a simple melody for nearly the entirety of the runtime, switching from a bass ostinato to a harmony ostinato midway through the piece. Furthermore, the first three songs are in the key of E minor.
"Burzum", the opening track, features a prominent melody played by a synthesizer that sits atop the distorted guitars and vocals. The two "Decrepitude" tracks compliment each other, with ".i." featuring vocals and keeping the guitars in the foreground; while ".ii." is instrumental and instead focuses on the sound effects and keyboard melody in the background of ".i.".
The album cover and booklet contain artwork by Theodor Kittelsen. The front cover is named Op under Fjeldet toner en Lur (Norwegian for "Up in the Hills a Clarion Call rings out").
Side A:
1. Burzum 07:05
2. Jesu Død 08:39
Side B:
3. Beholding the Daughters of the Firmament 07:53
4. Decrepitude I 07:53
Disc 2
Side A:
1. Rundtgåing av den Transcendentale Egenhetens Støtte 25:11
Side B:
2. Decrepitude II 07:52