The poet here speaks in the language of metaphor. (The preceding bolded word is a link to a wiki article on the topic; for further background, please click on it and review.)Originally Posted by hossein31
At first, the poet appears to be speaking about just a certain select group of people, i.e., "men who share the same room, soldiers or prisoners," but by the time we have reached the end of his one-sentence verse, we realize that his use of metaphor for the phrase, "the ancient community of dream and fatigue," (i.e., sleep, a nightly experience that all humankind shares) may be applied throughout his verse. And then with that realization, comes the idea that "men who share the same room, soldiers and sailors" is itself an (extremely clever) implicit metaphor. In other words, he wishes his reader to awake to the awareness of our common human condition; that we are all, metaphorically speaking, "men who share the same room, soldiers or prisoners."
With this depth in mind, one can follow each image of the poem as a metaphor for the human condition. What is the "armor" and "clothing" that we each wear and then, "fraterniz[ing]" through some "strange alliance," "cast off" "every evening," "over and above [our] differences?" This is the implied question that the poet is posing to the attentive reader -- through the language of metaphor.
The phrase you have underlined is a prepositional phrase that tells us where the nightly "fraterniz[ing]" he describes occurs.Originally Posted by hossein31