The most common and most likely answer to this crossword clue is the 14 letter word CONSTANTINOPLE
I've seen this crossword clue in The Times
C
O
N
S
T
A
N
T
I
N
O
P
L
E
More clues leading to the result CONSTANTINOPLE
- Old city has loyal citizens, in for exercise
- Mobile continentals getting work in Roman capital
- Old city displaced Pole chasing stable home
- Fixed work, in building line, means capital no longer used
- Old capital has loyal citizens in for exercise
- Fixed pole in ground 23 years ago
- Work secured by continentals relocated in ancient capital
- Fixed in pole, shifted to ancient city
- Ancient city plot’s on ancient ground
- No contest! Plain stupid old city
Buddy explains!
The straight part
We know that "Old city" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old city = constantinople.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.