City size limited to 6 when --> Monarchy

[Bromley]

I'm sure this is just a case of me being dim, but I'm having the following problem on Civ3 1.29f:

I had most cities at 5/6 and one at 7 (I had had another city at 7 previously, until I built a settler). I changed from Despotism to Monarchy. The cities with 6 population fill up their food storage but stop when full. The growth message changes to 9999 turns.

Any ideas what I'm forgetting?

[Finvola]

Are you building aqueducts?

[alva]

cities near rivers or inland lakes can go to 12 pop.
Other cities need aquaducts to go beyond size 6.

[Bromley]

lol. I am that stupid. Thanks.

[alva]

nope, that's what's called learning