Robert Plant wrote the lyrics about his travels throughout Morocco, Greece, and Spain. The music was inspired by Flamenco and Moroccan traditions.

The Greek mythology title refers to how Plant had a broken ankle (the Achilles heel), and was afraid of not being able to stand up again. Another mythical character, the titan Atlas, is brought up in the lyrics.

One of Led Zeppelins longest songs, running at a total time of over 10 minutes.