The Iroha is an archaic Japanese poem that was once used to order the kana syllabary. Its first known copy dates to 1079; at the time it was written, it contained each unique kana syllable exactly once. Since then, the language has changed in certain ways-- for example, the ん "syllabic n" kana did not yet exist, some of the older kana are no longer used, and several words have shifted in pronunciation-- and it has become more common in modern times to sort the kana in a more logical order based on the vowels. However, the Iroha order is still used in certain contexts such as notes of the musical scale or theatre seating.