Requiring immediate action, the old city goes on mildly (8)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
urgently
But I can't explain it at all! Could you help me understand?
(Other definitions for urgently that I've seen before include "As a matter of priority" , "without delay" , "Immediately, with pressing need" , "Earnestly and insistently" , "With speedy attention" .)