for this poem he employed the ancient english alliterative metre ( the verse form of beowulf and other anglo-saxon poetry ) , imposing on modern english the demanding patterns of stress and 'initial rhyme ' observed by the old poets : a skill in which he achieved great mastery , in very different modes , from the dramatic dialogue of the homecoming of beorhtnoth to the elegy for the men who died in the battle of the pelennor fields .