Heat melted both poles and capital (6)
I believe the answer is:
athens
'capital' is the definition.
(capital of Greece)
'heat melted both poles' is the wordplay.
'melted' is an anagram indicator.
'both poles' becomes 'ns' (north and south poles. I am not sure about the 'both' bit.).
'heat' is an anagram of 'athe'.
'athe'+'ns'='ATHENS'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for athens that I've seen before include "6 capital" , "City of the Parthenon" , "Mediterranean capital" , "Hasten to Greece" , "Capital of Greece" .)