"Tarkus" is the title track of Emerson, Lake & Palmer's second album. The progressive-rock epic lasts 20:35. It was the longest studio song by the band until the three impressions of "Karn Evil 9". The name "Tarkus" refers to the armadillo-tank from the William Neal paintings on the album cover. The artist has explained that the name is an amalgamation between 'Tartarus' (a place of punishment mentioned in 2 Peter 2:4) and 'carcass' (hence the name being written in bones on the album cover). Consequently, the name refers to the "futility of war, a man made mess with symbols of mutated destruction." The song "Tarkus" itself supposedly follows the adventures of Tarkus from his birth, through a fight with a manticore, which he loses and concludes with an aquatic version of Tarkus named "Aquatarkus". Keith Emerson, when asked what work he is proudest of, named his Piano Concerto (from the Works release) and Tarkus.

"Tarkus" itself is broken down into seven parts (timings reflect the beginning cues for each section):

The parts supposedly follow Tarkus' birth in a volcanic eruption centuries before known history. The exact nature of Tarkus' origin and actions are unknown, and left ambiguous by its creator, Keith Emerson. "Eruption" itself presents a musical impression of cascading eruption on the keyboards in a 10/8 time signature, backed by Carl Palmer on drums. This segues into the "Stones of Years", the first of three vocal sections.

The second, third, fourth and fifth are supposedly the movements that represent the enemies he meets:

According to Emerson, while Palmer was excited by some of the technical opportunities the song would present, Lake was not quite so enamoured, telling Emerson "If you want to play that sort of stuff, I suggest you play it on your solo album." The band almost broke up over the issue, Emerson telling Lake "Take it or leave it." The managers convinced Lake to stay and record the piece. Lake evidently did have the album grow on him, stating in an interview after the release: "But it's broader than that. The words are about revolution that's gone, that has happened. Where has it got anybody? Nowhere." He has also complimented "Stones of Years" as one of his favorite parts of "Tarkus", though he admits is not entirely sure about what it means, but says it is about, "listening, understanding, hearing".

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