The most common and most likely answer to this crossword clue is the 6 letter word THEBES
I've seen this crossword clue in The Times
T
H
E
B
E
S
More clues leading to the result THEBES
- Old city the one above all others? Not quite
- Ancient city, above all, unfinished
- Bet he’s out in the old city
- Ancient city he bets is in a destroyed state
- Not quite the perfect ancient city
- Some writhe besottedly in old city
- He bets foolishly in ancient Egypt
- Supreme, timeless ancient city
- Winners detailed in ancient city
- Most of the elite found in ancient Egypt
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 = thebes.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.