Around this time, Arion developed the type of poem called dithyramb, the progenitor of tragedy, and Terpander invented the seven-note musical scale for the lyre. For a short period it was a member of the Athenian confederacy, its apostasy from which is recounted by Thucydides in the Mytilenian Debate, in Book III of his History of the Peloponnesian War.