The most common and most likely answer to this crossword clue is the 8 letter word CITADELS
I've seen this crossword clue in The Daily Telegraph
C
I
T
A
D
E
L
S
More clues leading to the result CITADELS
Buddy explains!
The straight part
We know that "fortresses" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fortresses = citadels.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CITADELS mean?
CITADELS noun- A strong fortress that sits high above a city.
- (sometimes figurative) A stronghold or fortified place.
- An armoured portion of a warship, housing important equipment.
- A Salvation Army meeting place.