http://www.webexhibits.org/poetry/explore_famous_free_background.html
Extract
Ancient roots.
While free verse seems modernistic, its roots go back to medieval alliterative verse and even to the Bible. The Bible’s “Song of Songs” is written in what we would now call free verse. Many of the earliest Ancient Greek poets wrote in lines unmeasured by syllables and beat while they were developing what would become lyric poetry. In later Ancient Greece and Rome, however, fixed forms such as the ode, epic, and a variety of measured lyric poetry ruled the literary land.
How my heart sings 
Styles of poetry are also language-dependent. For example, rhyme is so easy in an inflected language, such as Latin, that metre become a more important element.
I think a point you made in an earlier post is also relevant – that poetry originally developed as an aid to memorising the ‘rules’ of society (very necessary before writing was invented). Any sort of regular pattern is very useful to achieving this aim.
We still find this usage in the plays of Shakespeare’s time, where the verse structure helps the players to remember their lines and the audience to follow the plot.
Now that literacy is widespread, poetry has acquired a different role. We enjoy the way a poet refines the language, to juxtapose different ideas in ways that excite our own thought processes and make us feel participants in the poet’s experience.
Yes,Mike, a very good point about what is possible in different languages.I think songs also enabled memory.I once read that singing predated speech.I also muse over the fact that before people could read privately they would hear stories or poems in public.Maybe books had as much effect as the computer has had in separating us from others.