At first, Xerxes and Nero arduously duel until idealised place (6)
I believe the answer is:
xanadu
'place' is the definition.
(I have seen 'Idyllic place ' mean 'xanadu' so perhaps 'place' could also mean 'xanadu')
'at first xerxes and nero arduously duel until' is the wordplay.
'at first' indicates taking the first letters.
The first letters of 'xerxes and nero arduously duel until' is 'XANADU'.
'idealised' is the link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for xanadu that I've seen before include "Winter palace of the Kubla Khan, according to Coleridge" , "Fabulous place" , "Where Kubla Khan built his pleasure dome" , "Where Kublai Khan built his pleasure-dome" , "Fabled wonderful place" .)