Sometimes I am limited to 9 armies in a city, sometimes I am not.  When the game does decide to limit me, I get the loud drum noise whenever anyone tries to move into (or through) that city.  

Perhaps I'm missing something, but in other cities and at other times in the same city I have been able to have multiple pages of units stationed.

(This is quite annoying as in this particular game my home city which also has my adventurer's guild is a choke point - so you can imagine how much hassle it is to move units from production towns to the front lines.)