A little while ago, I was looking for sentences for my RTK2 deck, and while attempting to find something for the character 伊 I stumbled across something that is, I suppose, near universal knowledge in Japan, but which I’d never heard of before – namely, the 伊呂波 「いろは」.

This Heian-era work is, to the best of my knowledge, the only poem that has ever become an alphabet.  It achieved this feat by containing within its seven lines every kana that was used at the time, once and only once.  It was originally written using the old system of using kanji to represent sounds only (a closely related practice survives to this day, known as ateji), and looked like this:

以呂波耳本へ止
千利奴流乎和加
餘多連曽津祢那
良牟有為能於久
耶万計不己衣天
阿佐伎喩女美之
恵比毛勢須

For which the kana were:

いろはにほへと
ちりねるを
わかよたれそ
つねならむ
うゐのおくやま
けふこえて
あさきゆめみし
ゑひもせす

Note the use of the archaic kana ゐ (wi) and ゑ (we).

The 伊呂波 was used as the ordering of the kana up until the Meiji reforms, when the modern system we are all familiar with was adopted.  Even to this day, some uses survive; interestingly, considering its origin as a poem, the notes of the musical scale and the files of the Go board are named according to the beginning of the 伊呂波.  As well, it is used as a sort of idiom corresponding to the English “ABCs” – indicating the fundamental set of knowledge in a given subject.

In English, it means something like:

Although its scent still lingers on

the form of a flower has scattered away

For whom will the glory

of this world remain unchanged?

Arriving today at the yonder side

of the deep mountains of evanescent existence

We shall never allow ourselves to drift away

intoxicated, in the world of shallow dreams.

translation: Ryuichi Abe

There’s quite a lot more information at the wikipedia article, if you want to dig further.