Early Anglo-Saxon Poetry relied not so much on syllable count, but on the number of stressed syllables per line. Middle English poets such as Geoffrey Chaucer moved towards strict syllable count, and the bulk of his Canterbury Tales was written with ten syllables per line. Aside from song lyrics French poetry at the same time was universally either in octosyllabic rhyming couplets (as in fabliaux or the tales of Reynard) or the heroic meter. Later forms of poetry began to use classical methods of writing poetry, and metric feet became the most important aspect of meter.
Because of the nature of the English language, metric feet were interpreted slightly differently to the way they were in Latin or French poetry. In English the most significant variation in speech is emphasis, so metric feet were based on which syllables were stressed. In French poetry syllable length was more significant, and so metric feet are based on where the longer syllables lie. Thomas Campion in his Art of English Poesie attempted to reform English poetry so that it relied on syllable length, but the variation in English syllable lengths is so small that he was ultimately unsuccessful in spite of the obvious benefits to musical lyrics.
Another feature often used in poetry is the caesura, which is just a pause in the middle of a line.
A Sixteenth Century Perspective
And in your verses remembre to place every worde in his natural Emphasis or sound, that is to say in such wise, and with such length or shortnesse, elevation or depression of sillables, as it is conmonly pronounced or used: to expresse the same we have three maner of accents, gravis, le[
No wight in this world, that wealth can attayne, "Unlesse he beleve that all is but vayne. \ / \ \ / \ / \ \ /
Also our father Chaucer hath used the same libertie in feete and measures that the Latinists do use: and who so ever do peruse and well consider his workes, he shall finde that although his lines are not alwayes of one selfe same number of Syllables, yet beyng redde by one that hath understanding, the longest verse and that wlnich hath most Syllables in it, will fall (to the eare) correspondent unto that whiche hath fewest sillables in it: and like wise that whiche hath in it fewest syllables, shalbefounde yet to consist of woordes that have suche naturall sounde, as may seeme equall in length to a verse which hath many moe sillables of lighter accentes. And surely I can lament that wee are fallen into suche a playne and simple manner of wryting, that there is none other foote used but one: wherby our Poemes may justly be called Rithmes, and cannot by any right challenge the name of a Verse. But since it is so, let us take the forde as we finde it, and lette me set downe unto you suche rules or precepts that even in this playne foote of two syllables you wreste no woorde from his natural and usuall sounde, I do not meane hereby that you may use none other wordes but of twoo sillables, for therein you may use discretion according to occasion of matter: but my meaning is, that all the wordes in your verse be so placed as the first sillable may sound short or be depressed, the second long or elevate, the third shorte, the fourth long, the fifth shorte, &c. For example of my meaning in this point marke these two verses:
I understand your meanyng by your eye. \ / \ / \ / \ / \ / Your meaning I understand by your eye.
In these two verses there seemeth no difference at all, since the one hath the very selfe same woordes that the other hath, and yet the latter verse is neyther true nor pleasant, & the first verse may passe the musters. The fault of the latter verse is that this worde understand is therein so placed as the grave accent falleth upon der, and therby maketh der, in this worde understand to be elevated: which is contrarie to the naturall or usual pronunciation: for we say understand, and not understand.