The servants of Don Vicente carried away his body, and Roque returned to his comrades, and so ended the love of Claudia Jeronima; but what wonder, when it was the insuperable and cruel might of jealousy that wove the web of her sad story?
There are no more uses of "insuperable" in the book.
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This objection would be insuperable if Homer had been an Ithakan.
Homer -- The Odyssey
I came to the conclusion that difficulties, well-nigh insuperable, lay between me and the safe possession of the beautiful little vessel.