Bas-relief, Persepolis. Close-up of a bas-relief depicting the Immortals in Apadana palace, Persepolis, Iran. The city of Persepolis was once the capital of the Achaemenid Persian Empire (the world's largest ancient empire), and dates from about 500 BC. It was founded by Darius the Great around 518 BC and destroyed by Alexander the Great. The ruins lie about 500 miles south of Tehran. The Immortals was the name given by Herodotus to an elite force of soldiers who fought for the Achaemenid Empire.