Why did I lose my city?

[Adriaticvs]

I'm really puzzled and would appreciate you helping me understand why I lost my city:

https://boardgamearena.com/13/catan?tab ... ayFrom=177

[Jontia]

I assume you're asking about Move 177?

Move 177 :06:22:22
Sova19 rolls dice: 4,2,Barbarians
Barbarians move one step further
Barbarians attack, win the battle and Pillage Catan with a strength of 4 against a defense of 3
Sova19 defended Catan with a strength of 2
Shersh315 defended Catan with a strength of 0
Adriaticvs defended Catan with a strength of 1
Barbarians move back to original spot
Shersh315 has no city (without metropolis) and is immune to attacks
Adriaticvs's only city has been pillaged
Knight is now inactive
Knight is now inactive
All knights are deactivated
Sova19 gets ore,coin
Shersh315 gets nothing
Adriaticvs gets grain

It's because the lowest strength defender has no cities.
Rules, see page 11

Important: When determining which player has contributed the weakest group of knights, do not count any player who has no cities or any player who has only metropolises. These players are immune to the effects of the barbarian attack.