The most common and most likely answer to this crossword clue is the 7 letter word POMPEII
P
O
M
P
E
I
I
More clues leading to the result POMPEII
- I’m Pope, I rebuilt an old Roman city
- Pipe assembly round mass blocks, one in ancient city
- Pageantry with European team in Italian city
- City buried English couple after ceremony
- Remains within easy reach of Naples
- Couple after Macedonian leader in Alexander, say, finding buried treasure in Italy?
- It could not cope with a burning issue of AD 79
- Translated poem in page 2 that was buried in Italy
- Ancient city failing to fulfil Portsmouth couple
- Show two under bottom of gravestone in old burial site?
Buddy explains!

The straight part
We know that "Ancient city" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ancient city = pompeii.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.