The most common and most likely answer to this crossword clue is the 7 letter word BABYLON
I've seen this crossword clue in The Times
B
A
B
Y
L
O
N
More clues leading to the result BABYLON
- Ancient city’s new life, with capital half revealed
- Youngster to yearn endlessly for ruined city
- Dear academic leaves city for 21 down city
- Little left, nothing new, in ancient place
- 14 Very young cat I lost in the old city
- Penniless Bob Dylan performance for ancient city
- Wonderful location girlfriend finds nearly remote
- Honey! Look north! It's a wondrous place!
- Tiny look over northern city of old
Buddy explains!

The straight part
We know that "ruined city" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ruined city = babylon.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 BABYLON mean?
BABYLON noun- A female breast.