You may have noticed that there there's not much form or meter happening in the poem. We don't see any rhyme schemes or regular meter, and the lines seem to be broken haphazardly (they aren't, as you'll soon see, Shmoopers).
Because it has no set rhythm or form, the poem is written in "free verse." This style of poetry gained in popularity after poets like Walt Whitman (another anti-war activist) adopted it, and its free-flowing ways were frequently utilized in the 1960s.
But that doesn't mean it's entirely free of style. Levertov kept the poem from looking like a paragraph by using enjambment, which means that the phrases continue to flow, bringing the reader along from one line to the next.
To see what we mean, try reading the following lines aloud (go ahead, nobody's listening):
It is not remembered whether in gardens
stone lanterns illumined pleasant ways (11-12)
See how "garden" flows straight into the next line's "stone"? This keeps the poem moving despite the line breaks.
But sometimes, Levertov might want us to take a breath. That's when she uses an end stop in the form of a comma or period. For example:
There is an echo yet
of their speech which was like a song.
It was reported their singing resembled
the flight of moths in moonlight. (27-30)
After "song" and "moonlight," you probably paused for a moment, visualizing (or hearing) the song and the moths moving around. The period is the end-stop that forces us to take a breath and think about what we've just read before we move to the next image or phrase.
Levertov's use of both end-stops and enjambment shows us that she wasn't haphazardly throwing it all together. Nope, she constructs the form in such a way as to direct our attention as we read. Check out "Sound Check" for even more sonic tricks that make this poem tick.