Poison in ancient city going round he got rid of (5)

I believe the answer is:

venin

This might be a double definition.

'poison' is the first definition.
(substance in venom)

'ancient city going round he got rid of' is the second definition.
The definition suggests a singular noun which matches the answer.

'in' acts as a link.

(Another definition for venin that I've seen is " Poison".)

I've seen this clue in The Times.

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