Most poetic how-to manuals start with syllables and feet, and tell you how to write a line
But in the kind of poetry we are exploring, neither syllables nor lines are basic.
What really matter are phrases: a special kind of phrase containing two natural heavy beats.
In poems like Beowulf and Sir Gawain and the Green Knight, every line contains two
of them; so they are often called half-lines or (more technically) hemistiches. But
all they are, really, are phrases: ordinary phrases of the kind we use in conversation all the time.
The best poetry always builds from simple, familiar language, and so it is here.
Consider the opening lines from my translation of Sir Gawain and the Green Knight:
The siege and assault having ceased at Troy
as its blazing battlements blackened to ash,
the man who had planned and plotted that treason
had trial enough for the truest traitor!
Then Aeneas the prince and his honored line
plundered provinces and held in their power
nearly all the wealth of the western isles.
Each of these lines naturally falls into two halves:
The siege and assault
as its blazing battlements
the man who had planned
had trial enough
Then Aeneas the prince
nearly all the wealth
These phrases, or half-lines are fundamental to alliterative poetry. They are the basic building
blocks. The very first thing you must do when writing this sort of poem is to learn to think in phrases.
Later I will go into more detail about how such phrases are built. (Not just any phrase
will do.) For now, just notice how these phrases, or half-lines, always seem to have two strong beats in them, though the number of syllables and the exact rhythm varies quite a bit.
Using phrases as its basic building block is something alliterative verse has in common
with many kinds of free verse. If there is an advantage in building from organic units of
meaning - and such phrases are by definition - then alliterative verse has that advantage.