Fortifications obstruct homes (11)

I believe the answer is:

blockhouses

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'fortifications' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Perhaps they are linked in a way I don't understand?

'obstruct homes' is the wordplay.
'obstruct' becomes 'block' (synonyms).
'homes' becomes 'houses' (I can't explain this - if you can you should believe this answer much more).
'block'+'houses'='BLOCKHOUSES'

Can you help me to learn more?

I've seen this clue in The Irish News.

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