Robust force from Spanish and Babylonian cities (6)

I believe the answer is:

vigour

I'm a little stuck... Click here to teach me more about this clue!

'robust force' is the definition.
'vigour' can be an answer for 'force' (vigour is a kind of force). I am not certain of the 'robust' bit.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for vigour that I've seen before include "Vital power" , "Active strength of body or mind" , "Energy, forcefulness" , "Force" , "Physical strength and health" .)

I've seen this clue in The Telegraph.

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