The poem opens quietly, almost meditatively. The speaker, a British soldier, observes the hush of the dawn in the midst of a World War I battle. But while daybreak is typically associated with life, hope, and renewal, here the poem establishes a subtle but palpable sense of unease.
Significantly, there is no description of the sun rising. Instead, the speaker observes through metaphor how the "darkness crumbles away." "Crumbles" is the important word here, suggesting decay, degradation, and destruction—all words that could apply to World War I and the horrors of humanity's supposed civilization.
The first line's meter initially suggests an iambic (da-DUM) rhythm, but this, too, "crumbles":
The dark- | ness crum- | bles away.
The extra unstressed syllable in the last foot, combined with the end stop, stifles the poem's momentum before it's even begun. It also creates a tense silence, into which the star of the poem—the rat—will appear.
In line 2, dawn, something that happens every day, seems to connect the speaker with the ancient world. That is, it links the soldiers of WWI, living in their frightening wartime present, with the "druid[s]," religious leaders in ancient Celtic culture. But this line isn't really about Celtic druids in particular; rather, the speaker is reaching back to find common ground with the people of the past, much as the poem will later meditate on the common ground between warring armies. Time itself is personified as a "druid"—ancient, eternal, and, perhaps, containing priest-like wisdom—in contrast to the absurd, murderous, present-day war.