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"fortress" is also used as a crossword clue. If that's what you saw, the answer is often stronghold (10 letters).
Definitions
a fortified defensive structure
Used in a sentence
“Like the Mesolithic age of 10,000-8000 B.C., the period 6000-4000 B.C. seems to be one of the fall of fortresses and the rise of pastoral nomadism.”
“Honour and Beautie in the owners armes, / Are weaklie fortreſt from a world of harmes.”
Source: Wiktionary, CC BY-SA 4.0
Used as a crossword answer1 curated clues
01“Stronghold”8 letters
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