Re: I was the King of the hill!
 

There are just two events that can spawn a fortress:

A local lord has built a fortress to defend his lands from revolting peasants.

The construction of a new ring wall defending a major city is completed. People from near and far are gathering to seek comfort and commerce in the city. Tax revenues have been permanently increased by 20 pounds of gold.

Lacking Excel on this computer I can not check which sites that spawn a fortress when detected or how common they are.

Re: I was the King of the hill!
 

Yeah the fortified city event is usually nice, but I got it once in a province adjacent to my home city and another major building fortress (both are not adjacent to each other) which cut down my available resource quit heavily...

...then again, it was later in the game and I did not need much resources anymore. I do not recall the actual scales, but given that it was in strong dominion, it must have been Order+3, Sloth+3, Growth+3, Cold+3, Luck+1 (or +2?), Magic+3 (Caelum). So Production is definitely not necessary for this event to happen. However, I cannot recall the actual luck score...