Queen from the south supporting what Catullus wrote for sex capital (6)
I believe the answer is:
vienna
'capital' is the definition.
(capital of Austria)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for vienna that I've seen before include "On the Danube, it was home to many great composers" , "Austrian city of the waltz" , "European capital" , "Wien" , "huge 20 [ULTRAVOX] hit" .)