I scout a level 23 city to discover minimal offensive and defensive light infantry forces and no scouts.

5 minutes later a force much more than sufficient to defeat this encounters massive defensive forces, the baltle report showed 7 war elephants, 250+ cavalry, 450 phalanx, 200 heavy infantry including 20 triarii and a smattering of light infantry similar to that  shown by the scouting.

Although the battle was recorded as a defeat approximately 40% of my forces returned having caused, according to the coalition challenge, just over 10K power points damage.

I returned with a much more powerful force 7 minutes later only to encounter a reduced light infantry force from the scouting, reduced by approx 40%

If these defensive units were from an ally why did I not see them in the scouting report?

It is possible they were sent by an ally in the 5 minutes between scouting and raid, but this hardly seems enough time to react, assemble despatch and arrive.

It is possible that the owner of the city had these troops hidden in the Acropolis and returned the remaining troops prior to my second attack but I am uncertain how a level 23 could own triarii.

Why, even though defeated, did a significant proportion of my troops return, I was under the impression that defeat was total and all units would be lost, this is the first occasion I've seen any different result.