Read "The Sea-Gods" at The Eldritch Dark:
This is a somewhat slight poem from Clark Ashton Smith (CAS), but it's interesting to compare the opening and closing quatrains:
Beneath the sunset and the sea
Their coral-builded cities be;
They keep an old forgotten reign,
A purple, far supremacy.
Known to their dim supremacy
The deep's forgotten secrets be;
Their old, eternal vestures are
The purples of the flowing sea.
Key items of repeated vocabulary ("forgotten", "purple(s)", "sea", "supremacy") between those two quatrains manage to capture the core of what the poem is about simply in those four words, given that CAS is using "purple(s)" in the adjectival sense denoting a being of royal rank.
While the noun "supremacy" speaks to power and rank, CAS alters the standalone meaning of that word with his choice of associated adjectives: "far supremacy" and "dim supremacy", echoing the notion that these sea-gods have known better days.
I think that CAS would have had a stronger poem on his hands if he had reduced "The Sea-Gods" to a single quatrain. Either the first or the last would do, although my personal preference is for the closing quatrain. I think the four quatrains in the middle of the poem are essentially filler, and perhaps CAS was also dissatisfied with this work, since he never included it in any of his published collections.