With tremulous cadence slow, and bring
The eternal note of sadness in.
Sophocles long ago
Heard it on the Aegean, and it brought
Into his mind the turbid ebb and flow
Of human misery; we
Find also in the sound a thought,
Hearing it by this distant northern sea.
The Sea of Faith
Was once, too, at the full, and round earth's shore
Lay like the folds of a bright girdle furled.
But now I only hear
Its melancholy, long, withdrawing roar,
Retreating, to the breath
Of the night-wind, down the vast edges drear
And naked shingles of the world.
The vowels in this line are themselves long and stretched to match the sense of sadness and depression.  The repetition of the noun “roar” from stanza one reinforces its importance.
Dover Beach