Let's talk Forts!
davepy over at the RON Heavens Forum asks about placement of castles and towers. It's an interesting discussion.

In 1on1, I usually place a castle directly behind my 3rd city. Since cities cannot be destroyed by enemy fire, the presence of the city helps protect the castle, while the (garrisoned) castle makes capturing a reduced city next to impossible. Castles might be nice to help push borders, but I find that they become juicy targets for enemy siege weapons.

I don't find towers to be all that effective, other than as an early warning system and to annoy the enemy. Singleton towers can be easily dropped by siege.
posted by Tim at 1:35 PM