Question

when the sun ____, the shadows must retreat
fleeing in fear from the fires of dawn.
the beacons never knew that its end was fleet
as a bright lord bears fires of flame.
the sun rises, yes -- but from the west it marching
rises eer eastward, eer eternal, eer bright.

Explanation:

To solve the fill - in - the - blank in the sentence "When the sun ______, the shadows must retreat", we can analyze the context and the overall theme of the poem:

Step 1: Analyze the context

The poem is about the sun and its relationship with shadows and the dawn. The later part of the poem mentions "The sun rises, yes -- but from the West it Marching / Rises e'er Eastward, e'er eternal, e'er bright". This shows that the action of the sun related to the retreat of shadows is the action of rising. Also, considering the subject - verb agreement and the context of the poem's theme (about the sun's rising and the effect on shadows), the most appropriate word to fill in the blank is "rises".

Step 2: Verify the fit

The word "rises" fits grammatically in the sentence "When the sun rises, the shadows must retreat" and also thematically with the rest of the poem which is centered around the sun's rising (including the non - traditional description of it rising from the west and then eastward).

Answer:

rises